Bullet Frass

Silver-spotted Skipper 1

Silver-spotted Skipper on Blazing Star

It may seem like an odd title for a post on one of our more common backyard butterflies, but I promise I’ll explain it in a moment. You may have seen this distinctively marked species as it darts about your yard from flower to flower. It is the Silver-spotted Skipper, one of, if not the, largest of our skippers.  Skippers are small to medium-sized insects in the family Hesperiidae. They are named for their fast, darting flight. Although more closely related to butterflies than moths, skippers more closely resemble many moth species in appearance by having stout, somewhat “hairy” bodies that are rather dull-colored.

Hoary Edge Skipper

Hoary Edge Skipper with tear in hind wing

For me, skippers have always been the sparrows of the lepidopteran world – those dull-colored, similar-looking small fliers that are difficult to tell apart. One reference put it succinctly – many species of skippers look frustratingly alike. Luckily, this species is a good one to practice your skipper observation skills on as there is really only one other skipper in our area that can be confused with the Silver-spotted Skipper. The Hoary Edge Skipper is slightly smaller and much less common than the Silver-spotted Skipper. A close look shows the diffuse white patch on the Hoary Edge Skipper is further back on the hind wing whereas the Silver-Spotted Skipper has the white more in the center of the hind wing.

Silver-spotted Skipper

Silver-spotted Skipper

The Silver-spotted Skippers are nectaring primarily on the Blazing Star and Bee Balm in the garden. They apparently almost never visit yellow flowers of which I have many species blooming right now.

Silver-spotted Skipper larva head

Silver-spotted Skipper larval head capsule showing false eye spots

But, as is often the case for me, it is the caterpillar which I find most interesting. Like most skipper larvae, they are rarely seen because they spend much of the day in folded leaf shelters and come out to feed primarily at night. The caterpillar chews and pulls together leaf fragments with silk to form a shelter. This provides some protection from many predators. When you do find one, the first thing you notice about later instar larvae are the bold orange false eye spots.

Caterpillar in leaf

Silver-spotted Skipper larva in exposed leaf shelter

But the really amazing thing is the other strategy they employ for avoiding predators (and hence the unusual title of this post). Studies have shown that many potential predators of caterpillars (such as wasps, who feed them to their own larvae) are attracted to the chemical cues in frass (the fancy word for insect poop). So, if you build a little shelter to hide in, you had better fling your frass out the door if you don’t want want hungry wasps to come knocking. Turns out these skipper larvae have a structure with the unpleasant-sounding name of anal comb. They use it to launch their frass pellets an impressive distance away from the shelter. One researcher showed that a 4-cm long Silver-spotted Skipper larva could launch a pellet an incredible 153 cm, or 38 times its body length. I’ve heard of tossing buffalo chips out west, but frass flinging? You just never know what potential new sport you might find right outside in your garden.

3 thoughts on “Bullet Frass

  1. Pingback: Eighteen new Dutch insect species | Dear Kitty. Some blog

  2. Thanks Mike. Silver-spotted skippers are so much fun to have around, and now I am even more impressed by them! I’ll have to see if I can catch a glimpse of this frass-flinging talent in action.

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