Home | Amphibians | Amphibian Declines – Pollution Worsens Disease and Parasite Attacks

Amphibian Declines – Pollution Worsens Disease and Parasite Attacks

Deformed FrogIn 1990, the IUCN’s Declining Amphibian Populations Task Force, to which I belonged, was one of the few large scale efforts addressing what is now known as the “Disappearing Amphibian Crisis”.  Today, with legions of biologists and hobbyists at work on the problem, we still do not fully understand why nearly 200 species have become extinct in the last 20 years – a rate 200x that of what might be “expected”.  But we do have some insights, one of which was highlighted in a recent journal article (Philosophical Transactions of the Royal Society (Biology) .  It appears that stress, much of which is in response to what we are doing to amphibian habitats, is worsening the effects of normal pathogens and diseases.

Parasites and Insecticides: a Confusing Scenario

As the reality of worldwide amphibian declines became apparent, herpetologists and private citizens began noticing increasing numbers of deformed and dead frogs. In 1995, school children in Minnesota made headlines when they found dozens of deformed frogs in a local pond. Since several chemicals are known to cause growth abnormalities, researchers began focusing on pollutants. At the Bronx Zoo, I worked with a veterinarian who studied African Clawed Frogs, and was amazed to see ovaries develop in males that had been exposed to Atrazine (a common insecticide).

But pollutants turned out not to be the whole story…a parasite also played a role. The creature involved needs to infect both a frog and a wading bird in order to complete its life cycle. Amazingly, it lives within a tadpole for a time and “re-programs” the development of the hind legs as metamorphosis occurs. The newly-transformed frog develops extra rear legs and, unable to jump very well, is likely to be caught by a heron – just as the parasite “intended”!

Actually, many parasites cause incredible changes in their hosts’ behaviors – one “directs” an ant to climb into the canopy and raise its now red-colored abdomen skyward in imitation of a tasty berry (so that it is eaten by the next essential host, a bird), another causes the host spider to build a silken shelter before dying, so that the parasite has a safe place in which to emerge, and so on…

Are Pathogens Changing?

Amphibians evolved some 300-400 million years ago, long before the dinosaurs, and they’ve likely been battling parasites similar to those described above for much of that time. The same can be said of other fungi, bacteria and viruses that attack them.

Yet it seems that certain pathogens and diseases, despite being around for centuries, are now causing unprecedented amphibian population declines and extinctions.  For example, Chytrid fungus, first identified as a serious threat in 1999, may be responsible for the disappearance of nearly 200 species. Although termed an “emerging disease”, it was likely present all along, but is now spreading more rapidly, and having a more devastating effect on its victims. This trend is seen among frogs worldwide (salamanders and caecilians are not as well-studied) – many pathogens are more common now than in years past, are spreading to new habitats, and are causing unusually high mortality rates.

The Role of Stress

According to the article referenced above, multiple stresses may be weakening amphibian immune systems, rendering them unable to battle common illnesses.  We see this in captivity all the time – animals that are assailed by inappropriate temperatures, hostile tank-mates or poor diets often fall victim to parasites and diseases that would have been handled by the immune system had conditions been ideal.

One stress factor can depress the immune system (in zoos, birds moved to a new exhibit often succumb to Aspergillosus infections, an ever-present fungus that typically causes no problems).  Currently, many amphibians are exposed to pollution, climate change, introduced species, habitat fragmentation and other stressors simultaneously. Small wonder that at least 2,500 species are believed to be in decline.

ChytridiomycosisPermeable skins that allow for the passage of harmful chemicals, and the typical need for two distinct habitats, predispose amphibians to difficulties when environmental changes occur. However, there is evidence that similar processes are at work among other groups as well (please see this article on snake declines).

What’s Next…What Can I Do?

Please be on the alert for deformed amphibians and signs of population declines, and post your observations here.  I can help you to get the information to organizations that can put it to good use.  Also, a colleague of mine is now involved in Amphibian Ark, a fine conservation group which can provide guidance if need be.

Please see the articles linked below for information on IUCN surveys and other efforts that utilize volunteers.


Further Reading

Frog Leg Trade Helps Spread Amphibian Disease  

Amphibian Study Seeks Volunteers 

Deformed Frogs Found in Minnesota

Bacteria may offer Chytrid Immunity

Global Amphibian Declines (excellent overview)

Chytridiomycosis image referenced from wikipedia and originally posted by Forest Brem


  1. avatar


    Hello, wanted to say first off, as many others have, how helpful your articles are.
    Walking home from work around 8pm on Sept 28th, 2012, I found a little frog hopping across the sidewalk. I still can’t believe I noticed him in the rain and dark, when he was so small. Less than 2in long, just a wee nugget. I brought him home, which some might say was my biggest mistake and even I am still conflicted about it. He was perfectly healthy, didn’t need me to take care of him, but every time I tried to put him back outside, he’d just sit on the ground and look so vulnerable.
    I live in MA, and when I was a kid we used to find tiny black frogs in Malden/Melrose, but I guess I don’t play in the woods and around ponds as much as I used to, because I rarely see frogs and toads ever anymore.

    Banjo (yes, that’s his name because I couldn’t think of anything else at the time and I used to walk a road through a swamp at night to get to work when I lived in Concord and the 1st night I heard what I thought was someone out there plucking a banjo. Then I heard another and another and nearly broke into a run. Banjo isn’t that type of frog and will never make those noises but it’s a decent enough name.), is only the 2nd of his kind I’ve seen alive and up close ever, in the town I currently reside, in central MA. The 1st was hopping through my boyfriend’s front yard so I just watched him hop away, a toad on a mission. I interrupted Banjo’s mission, which was probably to find a winter spot. I didn’t like that he was going to hop into the street tho. The most pervasive and disturbing experiences with frogs has been rainy nights on the road in a car. So I gathered some dirt and moss and sticks and a few bugs that came with the dirt, and made a temporary home for him in a plastic drawer. went online as he stared at me and am fairly certain he is an Eastern American Toad. Since he was so small, and there’s a pond near us, I suspect he might’ve been born there last Spring or Summer. I went back a few times to see if I could find any other toadlets or juveniles but too late in the year. I would’ve like to find another. If they were ever there at all. Also, his tailbone was sort of protruding when I found him, tho he wasn’t necessarily skinny. I thought it might be the remains of a tail, but can’t be sure. I don’t even know if Banjo is a boy or a girl. I tried to include a link to a recent pic of him, wondering if you can tell me. He (i just call him a he, it’s easier and nicer than “it”) has a black tie shape on his throat but a speckly chest and belly too. I suppose I will know when and if he starts singing. Also curious to go down to the pond in the spring and see what’s doin. I joke that I’ll bring him back down there and wait while he mates, then take him home again. I’m not at all sure about letting him go in the Spring. I’ve heard you’re not supposed to but if he’s a boy he’ll be calling, and if he’s a girl, she’ll be wanting to drop some eggs. He’s gotten bigger/longer and so much fatter these past few months. The pics are all up on facebook. I’m very proud of him, or her. As I have been, since I found him, I will proceed with caution and what’s best for him. Safe to say he’s under my care for the Winter, at least.
    He’s since upgraded twice and now lives in a 56-qt sterlite tub on top of my fridge. I was feeding him some wild caught insects like spiders and flies and grubs but worms were too big. I would sit outside with him on warmer days with his smaller tank and lid open and he ate a few ants if i held my hand as an elevator up to where they were climbing. I kinda knew then that my selfish heart wanted to adopt him. he has this cold, rubbery charm that I can’t resist. i had my first flower garden this past spring and summer, and there were bugs galore, but he couldn’t have those, or plants there as i’d used fertilizer and had used pesticide particles. I tossed his old dirt into garden that had mostly perished in a cruel early frost, and have been using the coconut fiber bricks as a 2-3 inch substrate. Changed it more frequently for the 1st month or so he was here. Less now because moving everything around seems stressful to him. All his holes and tunnels were gone and things all rearranged. So now I look for poop and shake dirt off of his plants, and change water daily. Also (and i’m not sure why i do this), I sometimes fluff up his dirt, making it softer for him and looking for any food escapees. Back to food: when i realized I was not going to be able to feed him right on my own, i ordered some phoenix worms and silkworms from mulberry farms online. the silkworms weren’t a hit; he ate 1 or 2 then no more and they ended up all dying. same story with phoenix worms. he ate 2 and that was it until recently when I brought the cup back out and collected the ones still living. suddenly, he liked them again. Before the worms i purchased got to me, I went to a convenience store in town and bought a tub of mealworms. but they were bigger than he was. Someone said I could chop off their heads but it seemed so ghastly, and he still might not eat it if it didn’t flail enough, so I put them out in my half dead garden. Crickets were the obvious next step, and he did love them. But they’re so fragile and jumpy and if I didn’t have a cleaner crew of bugs in there, I guess they could stink. Hard to manage anyway. My cat wound up with a few feeding time escapee snacks. They were good for dusting tho.
    Your articles clued me into vitamin A and calcium deficiencies, so i fed the crickets lots of carrots and kale and fluker’s orange cube diet with Zilla gut-load. then shook em in t-rex calcium no phosphorus with D3. I’ve since added roaches (baby dubia) to his menu, and reptivite. I put his roaches and crickets before I fed them all off (no more crickets! yay! my bf hates them.) in a salsa bowl with smooth sides, and seeing him eat is cute. The way he suddenly notices a bug and stares at it, then a little lunge and it’s gone. After re-reading about deficiencies and symptoms, I’m a little concerned about the lunging. I don’t see the tongue, but I just assumed it was there and fast. the only time he “missed” was when I was using a metal cat water dish as food bowl. He saw the cricket’s reflection and went after it. At that point I made metal bowl the water bowl and went on the hunt for reasonably priced opaque shallow smooth sided bowl. It was hanging up at the supermarket, haha.
    He doesn’t seem to have problems eating; in fact, the longer I have him, the more he seems to be able to eat. The roaches are his staple, and I even won a free roach breeding kid so in about a month he’ll have fresh babies. Once you get past the fear, roach husbandry is actually enjoyable. I’m fascinated watching them mature. They all eat organic roach chow from my new bug supplier, some cat food for protein and bran flake cereal for fiber (if it’s good for us, should be good for them!) They get their water from either water crystals or fruits and veggies i put in there. The babies seem to like the fluker’s orange cubes.
    This passed week, I tried again with mealworms, but from a guy off ebay. The price was reasonable and I noted that another customer of his was mad that they were too small to be “medium”. guess he wanted them as bait. But they were the perfect size for Banjo. All dusted up, he ate 7. The main draw for me is their ease of care, ability to gutload and hold onto supplement powder. Not as good at that as crickets but about the same, maybe a little better, than roaches. And they can be kept in the fridge if needed for a longer amount of time. Also purchased more phoenix worms from my bug people and was worried I was throwing away money again, because of the size and quantity I bought this time, but these were wigglier and meatier and he ate almost 20, in one sitting, with 2nds. The actual number was 15, because I was feeding out of the cup that seemed the oldest and removing the ones that looked dead. 15 is too many of anything, but he looked so happy. I feel pretty confident that this varied diet will get him through the winter. I rambled on and on, and none of this is about species preservation, other than my preservation of this specimen, while he’s under my care.
    Last but not least, my question: is it normal for a toad to climb a tree in his habitat? he started out just burrowing, making caves and tunnels, and burying himself up to the eyes. I felt like he was looking for a way out of that smaller bin I had him in. I’d find him sleeping with his belly pressed against the side of tank, but buried under the dirt behind him. Looking for security I guess. My biggest concern when I first started and still now, was keeping his stress down. In his big tank, I tried to make it as homey as I could. flat rocks in corners, little bio-degradable cup turned hut that he rarely went into before it degraded passed being useful for anything. I brought home a pink and green lily-pad lookin plant that I’d left at work outside of fish tank for the fish to look at. I knew it hadn’t been fertilized in 6mnths, just watered, so i put it in his tank along with some cheap plastic suction cup plants. Useless, except I have them hung around the top inside like a semi-canopy.
    One day he climbed the lily pad plant and just sat there, way up high. I was glad to see he could climb so well, but had never heard of toads doing this, so when hours had gone by, and he was still sitting there, I took him out of plant. He climbed back up a short while later. This was shortly after a full tank cleaning and I was afraid it had something to do with the water or dirt I’d used. Tap water, but I let it sit out to expand. Those fears were assuaged the next day when he was so buried in dirt I couldn’t find him. When I finally did, I felt bad about it and he went back up his tree. So I went to craft-store and purchased some clearance fake plants, different kinds, washed them and put them in there. Along with a rock I found that looks like steps and he looks like King Toad when he sits at the top. From what I can tell, he spends his evenings and nights either in or around food bowl, (there are two food bowls now, one for worms), then when he wants to go to sleep, goes up a tree. I can tell he’s sleeping cuz his breathing slows and his pupils slant almost shut. I’ve only seen him close his eyes when he doesn’t want to get poked in the eye or is swallowing. when he’s awake he has more of a round pupil with that lovely golden iris. this morning, after that big meal of maggots and a long soak in some warm treated water last night, I couldn’t see him but I found a monster poo. Was glad because I felt I hadn’t found many for a while. I know warm water helps them digest, and it’s worked right there in the water before (other times, he digs himself a shallow hole and does his business there.), but maybe the fiber bran stuff i have the mealworms eating might get passed on to him. or at least help him pass their rough parts. Anyway, I didn’t see him cuz he’d dug a new hole/cave under a tree. when I looked again, he was climbing the tree. It’s really cute, I just don’t know if other toads do this, too. I can only guess that maybe he feels more safe in the leaves and can look down on what’s happening down there. He never tries to jump out when i open lid and he’s on a high leaf. there’s plenty of airflow – numerous drilled holes in lid, but maybe that’s what he’s trying to get at, fresher air. His tank to me just smells like dirt, but not musty dirt. I apologize for all the mish-mash of information in this. I could talk non-stop about him and his bugs. And I have. Should I be concerned that he leans forward for his food? I think it might be due to being placed at the rim of bowl and having to get down in it a little bit cuz he’s still small. Should I be seeing his tongue come out and less movement from him? He rarely misses. Next feeding I will check. Feel free to browse his pics, they’re up on facebook and should be public. He’s gotten very fat, and grown, instead of hibernating. no heat source, just regular room temperature. he’s ok with infrequent handling, has stopped peeing on me. If this really was his first winter, and I didn’t let him find a winter home, in fact, abducted him and brought him to mine, would that throw him off, if I were to let him go in the Spring? I’d like to keep him for as long as I’m able to do it well. I’m quite fond of him, to put it mildly. Anyway, thanks. Without people sharing experiences and lessons learned the hard way, Banjo would’ve gone the way of Bud Wise and Er, that I briefly had in my care when i was 10. Not sure what happened to them, either i let them go or my mom got rid of them. Thanks to the internet (some of it), I’m not trying to give Banjo hamburgers and salads. Oh, one last thing, I’ve witnessed him shedding his skin twice. 1st time couldn’t see it very well but I knew what he was doing. The 2nd time I got a much better look and it was pretty gross. Slime hanging out of his mouth and all. Gross, but awesome. If you can make heads or tails out of anything I’ve said, then kudos to you. I had to take medication today that leaves me a little blurry in the head.

    • avatar

      Hi Crystal,

      Thanks for the kind words and your most interesting post….I can see you’ve put a lot of thought and work into the toad (cannot tell sex until adulthood, and you seem to be doing a fine job.

      They generally do not climb, but behavior changes in captivity; it may just be that, with less space to hunt and move about, the toad winds up climbing; I’ve seen this with other species.

      Good idea to leave burrows in place as much as possible, esp. as you seem to be taking care to clean up.

      Best to use an instant water de-chlorinator in water bowl and water used to hydrate the substrate. Sold as pet stores, for tropical fish, or I can send link to order.

      I’ve not used coco husk long term…should be fine, but best to limit possible ingestion by continuing to use a bowl for most feedings. Sphagnum moss is also good, hard to swallow, and they can burrow into it (although burrows do not stay intact).

      Add Reptivite or a similar Vitamin supplement, 3 or 4 times weekly.

      Roaches and phoenix worms are fine as a dietary staple, Earthworms are excellent; smaller ones are sold as red wigglers; avoid mealworms; high chitin content and associated with intestinal blockages; if you keep a colony, newly shed mealworms (white in color) are oK. Wild caught insects a very good idea.

      If you’ve not seen it, you might enjot this 3 part article on American Toads (Fowler’s toad care similar). At end of Part I, there’s also a link to an article on useful frog foods.

      Enjoy and pl keep me posted, Best, Frank

  2. avatar

    Thanks so much for responding to that! I know it was an eyeful and then some. Three and a half months of observations and questions stored up. I’ve read most everything I could find on american toads (not a ton out there) and frogs in general plus a lot of forum posts, but I’ve shied away of posting myself to avoid being chastised for toad-napping. It’s nerve-wracking to have a delicate little creature under your care that NOBODY else I know has or has had. Once I passed the point of no return (too cold), it’s been quite a bit of trial and error, and I’m trying to keep errors to a minimum, obviously.
    While I was writing I started thinking it really might be leaf cover he likes up in the plants. I’m thinking seriously of going back to craft store and picking a few more soft fabric “plants” and cutting off the stems more so that they become “bushes.” He’s missing low-lying plant cover. Selfishness on my part for wanting to see him. He’s so darn cute, but I’d rather he be comfortable.
    Unfortunate to hear coconut dirt might be bad, as I have three bricks of it left. I was concerned that on his 1st shed, he had some dirt on him and ended up eating it with the skin. His burrows and caves are darling; I had a feeling I should leave them be and would hate to give them up. He only sometimes uses the water dish as facilities and instead digs shallow holes in dirt. Scouting for waste is the main way I mess up his fine work. I will try to be more careful and keep a good eye on dirt ingestion. Had some real moss from backyard in there for a while and he enjoyed sitting on it (very soft) but it got dirty and after surviving a few rinsings had to be tossed.
    I’d like to share an experience I had with Reptivite. It’s more of a credit to the product than anything else, but it’s very fine and coats extremely well. I’ve shaken up too much with bugs and over-coated them, so that when he goes for them he just kind of flung them and winds up with it on his mouth like a messy kid with a powdered doughnut. I panicked that he didn’t have stickiness but he takes down lesser or non-coated bugs just fine. It says right on package to only use a tiny bit. The t-rex 2:0 calcium + d3 I have does not stick as well but also has vitamin A and was the 1st supplement I had on hand. Probably best to just get ReptoCal instead and alternate the two. (i don’t mind if you’re trying to sell the products, they are quality.) I use Repti-Safe samples for his water dish, but I am curious which marketed for fish you’d recommend. I was perusing the selection at Wal-Mart and gave up cuz I just didn’t know.
    I *think* his tendency to dart forward for food is more out of enthusiasm than tongue issues. But I’ll be keeping an eye on his aim. I read their vision is kinda bad up close. Dunno how true that is, but with the placement of their eyes I could believe it.
    My bf says I’m a total hover-mom when it comes to Banjo and it’s true. But I scooped up a healthy little toad so he needs to stay that way. I’m still carrying the guilt of the box turtle I had when I was 12 that didn’t live anywhere near as long as he should have. Now they’re hard to find, I feel awful and 17yrs later I still miss my turtle.
    I knew I was avoiding mealworms for a good reason, but it being winter, I wanted variety and shelf-life. Also ease of feeding, as in things that don’t climb or jump or burrow, or at least stay where you put them. The mealworm dish I have works to contain the phoenix worms too, as long as they stay dry.
    When I was 5 or 6 I collected all the earthworms I could find and built a spacious rock palace for them out in the yard. Came back the next day shocked that they were all gone. I’ve always been a little off.
    Banjo lived with a few worms I dug up for the 1st month or so he was with me and eventually they won their freedom, uneaten. In fact, I had a hard time getting him to notice food at all unless I placed him in smaller tupperware with a bug or two. He took down the fattest grub I’d ever seen in that fashion but one evening one of my cats (most dedicated bug hunter/eater i’ve ever met) noticed him sitting on desk with me and that quickly ended the practice. Then the 1st crickets I tried to give him I just dumped into his tank and when I didn’t see them anymore assumed he ate them but little buggers were hiding. Lost a bent beaked baby pigeon that way, assuming he was eating when he was only pecking. Horrible. Cabbed it to an animal hospital in Boston to have him put down. All the vets I called might as well have laughed at me.
    There was a point to some of that, besides sounding like a Dolly Doom… it was that I should give earthworms another chance now that I have a reliable method of feeding.

    Are you still caring for any American Toads or similar? And I’ve read about the toad who lived into his 30’s until he was accidentally killed, but do you know what the accident was? Or is that just internet lore?

    • avatar

      Hi Crystal,

      Sorry for the delay..computer probs; I’ll need to write quickly but will get back to you.

      Earthworms are one of the best foods to use. Please see “rearing earthworms…” article on my blog for some tips.

      You can use dead leaves as ground cover; this will lessen substrate ingestion also.

      We don’t know anything about their exact needs for Vits, etc; we go by expereinece only. Alternating is fine. CA, A, and D3 seem most critical , based on what we’ve seen.

      A number of toads, var species, have lived into their 20’s and 30’s. 2 Marine Toads I cared for at the Bx Zoo came in as adults and were still going strong at 25 yrs. Young animals more difficult to care for, as nutritional needs critical at that point.

      Reptisafe is fine if it removes chlorine and chloromines…otherwise any brand marketed for tropical fish (same ingredients used for all).

      Enjoy, Frank

About Frank Indiviglio

Read other posts by

Being born with a deep interest in animals might seem unfortunate for a native Bronxite , but my family encouraged my interest and the menagerie that sprung from it. Jobs with pet stores and importers had me caring for a fantastic assortment of reptiles and amphibians. After a detour as a lawyer, I was hired as a Bronx Zoo animal keeper and was soon caring for gharials, goliath frogs, king cobras and everything in-between. Research has taken me in pursuit of anacondas, Orinoco crocodiles and other animals in locales ranging from Venezuela’s llanos to Tortuguero’s beaches. Now, after 20+ years with the Bronx Zoo, I am a consultant for several zoos and museums. I have spent time in Japan, and often exchange ideas with zoologists there. I have written books on salamanders, geckos and other “herps”, discussed reptile-keeping on television and presented papers at conferences. A Master’s Degree in biology has led to teaching opportunities. My work puts me in contact with thousands of hobbyists keeping an array of pets. Without fail, I have learned much from them and hope, dear readers, that you will be generous in sharing your thoughts on this blog and web site. For a complete biography of my experience click here.
Scroll To Top