Reader Mark Sturtevant has another great batch of arthropod photos. I’ve indented his notes. Be sure to see the vestigial legs of the butterfly in the last two photos. I had no idea that some species had vestigial legs!
Here are pictures of arthropods taken during the winter and early spring of last year. A snowy winter day might not be considered a time for arthropods to become active outdoors, but various species are out and about even when there is snow.
One well known example are the tiny (tiny!!) black springtails that gather around tree trunks and exposed rocks during the latter half of winter. Springtails are a group of small arthropods that are not considered true insects even though they have six legs and antennae. They can jump with a muscular extension from near the rear of their abdomen. I presume the species that is shown is Hypogastrura harveyi. These can gather in the high thousands, peppering the snow in their numbers as can be seen in the associated link. My highest power lens was pushed toward its limit to take these pictures since these little critters are less than a millimeter long. Hard to find in the viewfinder too!
The next two pictures represent some of the insects that can also be seen during the winter or early spring. First is a sawfly (which is a kind of wasp) Dolerus unicolor, and next is a caddisfly. I have no idea of the species, but caddisflies are in the order Trichoptera (meaning “hairy wing”), and they are a sister group to the “scaly wing” Lepidoptera (the butterflies and moths). Their similarity to moths is pretty clear. Caddisfly larvae are also pretty similar to caterpillars, but they are usually aquatic. Most larvae in this order build a shelter out of twigs or sand grains, and they crawl around carrying this shelter with them. Some examples are here.
Anyway, different species emerge as adults at different times of the year, and they often swarm near water. Well before leaves were really coming out last spring, a local river had many hundreds, perhaps thousands of these insects fitting about on the branches of trees that overhung the river. Every twig was festooned with them. I was not completely happy with the pictures, so I came back within the week for another attempt. But because these insects are notoriously short-lived as adults, by then they had all vanished.
Before the main photography season begins in earnest I like to practice by visiting a local butterfly house. The final pictures were from one of these visits. The first is of a blue morpho (Morpho peleides), which is generally regarded as the star of most butterfly houses. They attract a lot of attention since they are among the largest butterflies in the world and they flash iridescent blue wings when in flight. They are good at disappearing when at rest since then they usually hold their wings tightly closed. This one was feeding from a rotten banana that was set out for the butterflies.
The next picture is the aptly named malachite butterfly (Siproeta stelenes), a species that ranges into the southern US.
Butterfly houses commonly stock several species of ‘long wing’ butterflies. These small butterflies come in a bewildering array of species, and many of them have different colors in different parts of their range as they have evolved to resemble another species of butterfly in complex systems of Batesian and Müllerian mimicry. The last pictures are of the tiger longwing (Heliconius hecale). Note in the first picture that this butterfly has a vestigial pair of front legs that are immobile and pinned to the thorax. This is actually very common among butterfly species. I suspect the reason for this is that since butterflies really only use their legs for perching and not for walking, it makes sense to vestigialize a pair of legs to reduce weight. Perhaps “vestigialize” is not a real word, but it does make sense.
I understand what is said about the springtails – I only learned about them a few years ago when a tarp I own was left outside. I discovered a black coating that was moving on it – it took a while to understand there are jumping tiny (tiny!) animals on it.
Cool set overall.
Wow you can see the hairs on the springtail – that is an achievement I think.
The “Blue Morpho’ is actually an Owl Butterfly. Caligo memnon.
That is correct! The big thing never did open its wings.
A 2011 study on fore-leg reduction in butterflies can be found at the link at the bottom. The answer to why leg reduction has occurred seems to be that the legs have been shunted into a specialized chemo-sensory function in which sense organs detect sugars (both sexes) and specific odors and “tastes” that characterize host-plants suitable for oviposition (females). I suspect four legs are as good as six for supporting a butterfly when it lands and that losing a pair of functional legs does not much affect over-all adaptation.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3281478/
That is interesting. I have read in various places that the front legs have that role anyway, and it is common knowledge that ‘butterflies taste with their feet’. But I can see how expansion of their role for olfaction would mean it is not necessary to be able to extend their legs in order to directly ‘taste’ things.
Mark, females test host plants using their forelegs, which, although reduced in size, can still be extended. The legs probe the leaf epidermis and, I suppose, assay underlying tissues. In the field it is often possible to hear the forelegs tapping, as a drumming sound, each time a female touches a host-plant leaf.
Only two butterfly groups show foreleg reduction. In the Nymphalidae — the butterflies in your photos — leg reduction occurs in both sexes. I suppose, but have no evidence, that the legs of the female evolve to become short, stout, and muscular as a specialization. In contrast, only male Riodinidae have evolved reduced forelegs. Don’t ask me why.
Here is an article on the role of drumming in rapid host-plant recognition:
Sabrina Thiele et al. 2016. Oviposition in Heliconius erato (Lepidoptera, Nymphalidae): How Essential Is Drumming Behavior for Host-Plant Selection? Journal of Insect Behavior. 29.
Thank you for photos and information. The information about the vestigial legs is fascinating. Without this website and this post, I would never have found this information out-
Thanks!
The earliest members of the Springtail family (order?) were identified some time back in the 1990s from a volcanic spring deposit at Rhynie in Aberdeenshire dated to about 410 Myr ago.
Some of the nearby large granite batholiths are slightly younger in their argon-closure dates, so it was plausibly vapours from the cooling magmas which cooked the spring waters.
The photos and commentary are great. Thanks for sharing and teaching. To me, springtails are kinda cute.
Very nice. I assume that what looks like a coiled hose under the head is a very long set of mouthparts.
Last summer we had tons of moth-like flies along the Snake River. I’m thinking, now, they must be Caddisflies.
Beautiful and interesting!
Fantastic set. I look forward to seeing more of your photos as you come into the peak photography season and we in Australia leave it.