Posted on 07/31/2005 5:51:47 PM PDT by furball4paws
A snail eating caterpillar is described. It hunts down snails, ties them down with silk and devours them.
"Such oddball lifestyles tend to develop in isolated ecosystems where there's a limited variety of creatures, as in Hawaii. "There's more room for evolutionary experimentation," says Gillespie. For example, Hawaiian insects evolved without ants as predators or competitors for food."
(Excerpt) Read more at sciencenews.org ...
Always asking for one. Just got back from a walk, and he is now a happy camper. He had a bad case of cabin fever. It was raining today, so he was cooped up and the family was all out celebrating my youngest son's baptism. He is 10. (I got to baptise my own son. Proud daddy.)
Doesn't sound like fun to me.
Many Years to your son! (Orthodox congratulatory message)
Whoa. Is that the same species?
Me too. I am serious. Do you think this is something we can look into? I hate the dang slugs here with a passion.
Are you near Seattle?
No. I think it's another kind of caterpillar.
So far, the only thing I have been really happy with is the Corry's slug bait.
Kills em deader than doornails.
Yep. That catepillar just eats pancakes.
Ain't no ants in Hawaii?
Wow, learn sumthin new every day.
That's an absolutely extraordinary thing, if true.
If there are two type of species that IMHO rule the planet, it's ants and birds.
Keep in mind that snails are voracious plant-eaters too. Most gardeners find snails/slugs a more destructive pest than caterpillars. It's not a big leap from eating others of your kind when you encounter them as "competition" on your hostplant, to eating *other* invertebrates you find on the same plant for the same reason. I'd bet a reasonable sum of money that the snails are common "predators" on the same hostplant that this caterpillar's ancestors used to feed on. The snails may have been bigger "competition" for food than others of the caterpillar's own kind.
Eventually it may have turned out to be more productive to take a step up the food chain and just specialize on eating the snails exclusively.
Or maybe not exclusively. The article doesn't mention whether the caterpillars eat snails *exclusively*, or hunt them in *addition* to still eating the ancestral hostplant. From the description, it doesn't sound as if they've been studied in the wild much. That may still be an open question. And it seems a *long* evolutionary road from being an obligate vegetarian to an exclusive carnivore, even among insects. Such a drastic change in diet requires a lot of biochemical adjustments. Mixed diets are a lot easier to adjust to, since you can still get essential nutrients from your ancestral foodsource, and don't have to "switch" over to getting *all* of them from a completely different kind of diet.
In any case, a scenario like the one above seems a much more plausible evolutionary pathway than just starting from a plant-eating ancestor, and then *bam*, becoming snail-hunters in "one step".
As for how caterpillars started eating others of their own kind, when they were "built" for eating plants, some have hypothesized that it's not that big an innovation, since other eaters of the same hostplant may well "smell" or "taste" like the hostplant which the caterpillars are primed to chemically recognize and consume anyway. Most caterpillars are highly selective about their hostplants, and seem to have specific chemical "triggers" which tell them which plants are suitable hostplants and which ones aren't. Another caterpillar (or snail?) which has been eating the same hostplant may well be exuding the same chemicals which it has incorporated from its own meals. Caterpillars aren't all that bright, and anything which "smells" the same may be considered an acceptable meal, even if it's not green and leafy.
I saw a possible instance of this the other day. Monarchs aren't normally cannibalistic, and large dense batches of them (denser than would ever be found in nature) can be raised on the same milkweed without noticeable mortality -- they just climb over each other. But the other day I saw one Monarch caterpillar eat the "feeler" off another one, in exactly the same manner it would have eaten a sliver of milkweed. I think it was just keying off the same alkaloids it uses to recognize milkweed itself, which Monarch caterpillars concentrate in their own bodies in order to make them distasteful to predators like birds.
Nor have I ever seen a Monarch (or any other caterpillar) "experimentally" eat anything other than its appropriate hostplant, so that explanation for the "feeler eating" is unlikely. Caterpillars will starve to death rather than eat (or even attempt to eat) a plant not on their "genetically approved" list. If it doesn't have the right chemical triggers, it just ain't food, as far as they're concerned. We lost two batches of Spicebush Swallowtail caterpillars until we realized that what was sold to us as a spicebush plant by a usually reliable nursery wasn't actually spicebush. The caterpillars all just failed to eat, and died. Even some hybrid varieties of their actual hostplant will be refused by caterpillars, apparently they don't "smell" right. This is a common problem with Pipevine Swallowtails -- many hybrid pipevine varieties favored by gardeners are rejected by the caterpillars, which is a real shame because the *adult* Pipevine Swallowtails often recognize them as suitable hostplants and lay eggs on them, but the *caterpillars* don't, and subsequently die of starvation. Apparently the adults and the caterpillars use somewhat different "recognition" systems -- not surprising, considering their difference in physiology. But the end result is that a lot of Pipevine Swallowtail eggs get "wasted", which may be one of the reasons that they are rather rare, especially compared to the success stories of the other swallowtail species.
But I digress. My point is that while caterpillars would be expected to make "chemical recognition mistakes" and occasionally eat other consumers of their preferred hostplant, natural selection would likely only encourage serious cannibalism in species where hostplants are more likely to be totally consumed by overly large broods. This could explain why some species are frequent cannibals and others aren't. And a similar mechanism could easily have led this particular moth species into a situation where it was eating snails in the first place (due to chemical miscues caused by eating the same hostplant), and was also under selective pressure to wipe out as many snails as it could (if the snails frequently caused the caterpillar's hostplant to end up denuded of leaves before the caterpillars could finish their fifth instar and pupate).
I can't think of a more plausible evolutionary scenario (heck, I can't think of *any* scenario) by which the caterpillars would by some other means make the leap from eating plants in their ancestral form, to going after snails in a serious way. It seems especially unlikely for caterpillars to begin eating snails by some other scenario when you consider just how highly selective they are in their eating habits -- if they don't even eat other plants that don't "smell" right, even hybrid plants of the same genus, how would they start going after snails by any scenario *other* than the sort of "tastes the same due to food competition" scenario mentioned above?
I think that most interesting is if there is some method to where the moth lays its eggs, say to increase the chances of finding a snail (doesn't say if any old snail will do or if only certain kinds are prey).
See above -- if the snails frequent the same ancestral hostplant, the adults don't even need to change their egg-laying habits. Laying on the same hostplant places the eggs in proximity to the snails which the caterpillars now eat.
As you know ichneumons lay their eggs directly in(on) their prey. That certainly means that some will be successful. Perhaps the reason is in the lack of insect predators in Hawaii, so they can be slow and allow for many "misses" and still be a successful species.
True -- insects have a general reproductive strategy of making up in quantity what they might lack in individual success rates. Butterflies and moths typically lay upwards of a hundred eggs per female. They can afford to lose a few and use a "spray and pray" methodology.
Oops, meant to ping you to my #74. Feel free to add your critiques.
"A snail eating caterpillar"
Where can I get some of these? The damn snails are eating my tomato plants.
Yep we could all be millionaires soon. We just have to figure out how to get started.
See, almost 80 posts on a thread of snails and caterpillars. Of course only Ichy really talked about the science of the thing, but what do you expect?
Ichy: I appreciate your view especailly with the personal observations. Since we don't know how they eat in the wild and whether they are exclusively meat eaters and whether they only like certain snails, much is speculative.
But I think there is much more to this phenomenon than eating the same thing that eats your food. The fact that these caterpillars appear to hunt snails. And how would they develop the ability to nail them down with silk before eating? If the snails just smelled right and got chawed as a result, the immobilization does not make as much sense. What we need is for someone to find an intermediate species. WHY ARE THERE NO TRANSITIONAL FORMS!
This is one of those things that will sit in the literature for a long time before anything new will happen.
There was an earlier mutation where the caterpillars attempted to use a lasso to catch the snails, but due to the caterpillars' unfortunate lack of arms and hands, it wasn't successful, so those mutants went extinct.
The pic was taken the first thing in the morning as this moth was still flying around and then it landed in the bush upside down where I suspect it was going to remain until that night. Bugs are cool, I made a bad career choice 37 years ago..........
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