#prolegs

I’m sorry it’s been like, a year or two but I must deliver worm content again.

Heyo! I know you’re not in Australia, but there was a whole group of caterpillars (I guess?) by the edge of a path on a nature walk today. They moved as a group, and had little pointed butts that they tapped on the ground when my partner and I got close to them. I tried identifying them, but with no luck, so I wanted to see if you knew them? Thanks in advance, regardless!

LOOK AT THESE CUTE LITTLE BABIES!!! You are right to be a little suspicious of these guys. There aren’t any clear shots of their little suction cup prolegs because they are all in a huge pile together (when they’re in groups like this, they’re called “gregarious”). If you did pick one out and take a good look at it, you would likely be a little more suspicious.

Here is what you would see for a typical caterpillar:

This is a Gulf Fritillary caterpillar, just after molting. I numbered the prolegs. There is a little variation, like with inchworms (who only have two!), but for the mostpart, the most you will see is 5 (the exceptions are the slugmoth caterpillars, but you will never confuse them with these next guys).

Here’s what you would see if you pulled out one of your little friends there:

Here’s a freshly molted baby! Hmmmmmm.

Here’s another baby! Wait a minute...

Your friends are not baby moths or butterflies, they are the babies of:

A sawfly! Related to Bees, Wasps, and Ants!

Of course, I only have photos of the Texan ones, and I honestly haven’t seen too many species (these are not easy to find here!). But oh boy, the Australian sawflies are beautiful! 

Your sawfly larvae are in the genus Perga. Here is what the adults look like (2 cm long and beautiful):

Image from iNaturalist, copyright Felix Fleck [link]

How did I figure this out? I googled “Australian caterpillars,” and landed on this page: The Identification of Caterpillars of Australia [link]. Large caterpillars are noteworthy, especially gregarious ones. But they’re not on the main page. The long legs (actually legs, up front) made me suspicious as well, so I clicked over to their sawfly page [link], and there they were! I looked them up on iNaturalist, and we were in business.

Thanks for asking, that was fun! I didn’t realize sawflies got so big (but of course they do!)

That is all

stephyra17 submitted:

Hi! So I found this in my recycling bin, fondly called it Morpheus but I don’t know what it is exactly, like I know this is a cocoon but is it from a caterpillar? Or moth? Maybe silkworm (i assumed it was a caterpillar but now I’m not sure after looking at caterpillars cocoon, they don’t have that white “silky” envelope) thank you!! I’m from Canada if that helps you more

Nice find! I had to do a bit of research for this one, since I didn’t immediately recognize it. I’ll give you the “what is it?!” answer first:

This guy! This is a Tent Caterpillar. They are in the Malacosoma genus [link to bugguide page], and there are three species occurring in Canada. Depending on where you are in Canada, you may have two or three of these species, but one species occurs in all of Canada and the US. That species is the Forest Tent Caterpillar Moth, Malacosoma disstria, and that is also the species in my photos. Tent caterpillars will build large communal webs that can engulf entire branches of trees (webworm moths also do this, so don’t think all these webs are tent caterpillars!). When they are ready to pupate, they wander off on their own and fine a nice safe area to start spinning a cocoon.

This photo shows a Forest Tent Caterpillar who found a nice corner on a leaf and has already put down that protective webby layer before spinning his cocoon. When he’s done, he will look exactly like your photo, where you see the cocoon under the sheet of webbing. If you were to remove the webbing, you would see the cocoon, which is a very dense, tightly spun structure. These things offer a lot more protection than you would think!

When they are done cooking, they pop out looking like this. CUTE! <3 <3 What a handsome fluffy boy! This is a male Forest Tent Caterpillar Moth.

Your other questions are good ones, too! A lot of the terminology with entomology can be confusing, especially with contradictory “common names” for insects (common names are what people actually call them, as opposed to scientific names that are unique to each species regardless of location). An example: webworms and silkworms are both types of caterpillars, not worms. Just like fireflies/lightning bugs are neither flies nor bugs (they are beetles!), and potato bugs are either beetles or isopods depending on where you live.

But what is a caterpillar anyway? The easy answer is: a caterpillar is the larval life stage of butterflies and moths (order lepidoptera). Except… 

The first time I saw these things, I was hella confused. Wtf is this thing? It looked like the illegitimate child of a cursed love affair between a Polyphemus moth and a June Beetle.

Above: Polyphemus moth caterpillar (Left) and Scarab larva (right)

It turns out, my mystery larva is a Sawfly Larva. These can be easily confused with Moth/Butterfly Larva because they essentially look the same (and also, have you ever even heard of a sawfly before???). Also, even worse: both can be called caterpillars. 

Above: A caterpillar. Guess which kind! (Hint: it doesn’t turn into a moth or butterfly)

I think it’s ridiculous to call both caterpillars, so I’ll stick to using “caterpillar” to refer ONLY to baby moths/butterflies. The best way to tell caterpillars and sawfly larvae apart is the number of prolegs. With one or two exceptions, all caterpillars will have five or fewer pairs of prolegs. Sawfly larvae always have more than five. But wait, you may be asking what the heck is a proleg?!

These. These are prolegs. I used a Cecropia caterpillar as an example because they are SO LARGE and have exceptional chubby prolegs (also, Cecropia moths are a type of silk moth!). Prolegs are the little warty suction cup-type things caterpillars (and sawfly larvae) use to keep their fat pudgy bodies from falling off everything they try to hold onto. They only have three pairs of legs (just like the adults!), and those are the pointy things you see on the front end of their bodies. Caterpillars can have fewer than five pairs of prolegs, inchworms (again, NOT a worm!) being a notable example–they only have TWO pairs!

To address your other point (what do caterpillar cocoons look like?), well, there are a lot of moths and they all make different types of cocoons. 

Some cocoons! Left to right: Withered Mocis (makes cocoon out of blades of grass), Psara dryalis (makes cocoon out of a single leaf), Tussock moth (sheds its caterpillar hairs and glues them together with silk)

Some more cocoons! Left: Southern Flannel Moth (they spin a thin silk layer, then within that, spin a much denser layer, complete with a door flap I’m not joking), Right: Virginian Tiger Moth (sheds caterpillar hairs, loosely binds them to make a fragile cocoon).

Also, not all moths make cocoons! Some will just pupate wherever they happen to be and hope nobody finds them and eats them! Also: butterflies do not make cocoons (the pupa is always inside the cocoon–the cocoon is just the protective layer), and butterfly pupae are called chrysalids (singular: chrysalis).

Thanks for your questions, they were good ones! :D