More Mayslake Insects

by Carl Strang

As we progress into the warm season, more and more insects jump, fly or climb into view. Most of the recent photographic subjects at Mayslake Forest Preserve have been moths or butterflies.

Monarch butterflies have received a lot of attention lately. Here a nearly mature caterpillar nibbles at a common milkweed flower.

Monarch butterflies have received a lot of attention lately. Here a nearly mature caterpillar nibbles at a common milkweed flower.

The beauty of moths is more subtle. This one is called the confused eusarca, a member of the inchworm family.

The beauty of moths is more subtle. This one is called the confused eusarca, a member of the inchworm family.

The prairies and meadows have produced dozens of tiger moths in the genus Haploa. These all seem to belong to two species.

I identify this one as a reversed haploa. A dark line extends from the midpoint of the leading edge of the forewing to the back corner of the wing.

I identify this one as a reversed haploa. A dark line extends from the midpoint of the leading edge of the forewing to the back corner of the wing.

This one appears to be a LeConte’s haploa. Here the dominant line goes out from the tip of the wing.

This one appears to be a LeConte’s haploa. Here the dominant line goes out from the tip of the wing.

Each species is represented by an array of confusing variations on these themes.

It hasn’t been just about moths. Here a Batyle suturalis longhorn beetle visits an ox-eye daisy.

It hasn’t been just about moths. Here a Batyle suturalis longhorn beetle visits an ox-eye daisy.

The most dramatic recent insect observation was this Laphria robber fly, with its prey, a honeybee. Laphria are bumblebee mimics.

The most dramatic recent insect observation was this Laphria robber fly, with its prey, a honeybee. Laphria are bumblebee mimics.

Mayslake Update: Insects

by Carl Strang

The warm weather has brought out a beautiful diversity of insect life at Mayslake Forest Preserve. Here’s the gallery from last week:

Early zanclognatha moths are appearing in good numbers this year in Mayslake’s woodlands.

Early zanclognatha moths are appearing in good numbers this year in Mayslake’s woodlands.

Here is a second one, showing some of the variation in this species.

Here is a second one, showing some of the variation in this species.

What they have in common is their relatively early season compared to similar relatives, a rather sharp bend in the dark line closest to the head, a kink or at least flat area in the tip of the curve in the middle line, and a rather straight outermost line. This is one of a large group of moths whose larvae make their living by eating dead leaves. Many are common in our woodlands thanks to that abundant resource.

This skipper put me through a long session with the references. I concluded that it is Juvenal’s dusky wing.

This skipper put me through a long session with the references. I concluded that it is Juvenal’s dusky wing.

It is very similar to the wild indigo dusky wing, which also occurs at Mayslake, and I need to be more careful in the future in identifying these butterflies. The difference, as I understand it, is that Juvenal’s has areas of pale color within the black inner part of the forewing, and just inward of the central tan area there is a pale dot (very faint in this individual) rather than a short bar.

Less ambiguous is this Virginia tiger moth. There are other white tiger moths, but they don’t have the fancy black-and-white barred legs, a couple of which are sticking out here. Also, this one patiently let me move its leaf so as to get a look at its front femurs. They were yellow-orange rather than pink.

Less ambiguous is this Virginia tiger moth. There are other white tiger moths, but they don’t have the fancy black-and-white barred legs, a couple of which are sticking out here. Also, this one patiently let me move its leaf so as to get a look at its front femurs. They were yellow-orange rather than pink.

This pretty little moth, photographed near the edge of the north savanna, was an addition to the preserve species list. The spotted grass moth is described as “uncommon” in references.

This pretty little moth, photographed near the edge of the north savanna, was an addition to the preserve species list. The spotted grass moth is described as “uncommon” in references.

Viewed dorsally, this Laphria thoracica robber fly is a very effective bumblebee mimic. At this angle, however, we can see how it is alertly watching for passing prey. The flattened abdomen, impressive predatory beak, and odd antennae prove that this is no bee.

Viewed dorsally, this Laphria thoracica robber fly is a very effective bumblebee mimic. At this angle, however, we can see how it is alertly watching for passing prey. The flattened abdomen, impressive predatory beak, and odd antennae prove that this is no bee.

First spreadwing damselfly of the year. The southern spreadwing is regarded by some as a subspecies of the common spreadwing.

First spreadwing damselfly of the year. The southern spreadwing is regarded by some as a subspecies of the common spreadwing.

Bumblebee Mimics

by Carl Strang

There are mimics, and there are mimics. A couple years ago at Mayslake Forest Preserve I found a syrphid fly that mimics bumblebees.

This is the narcissus bulb fly, Merodon equestris.

This is the narcissus bulb fly, Merodon equestris.

It was comparable in size to a small worker bumblebee, though none of our local bumblebee species match this color pattern, and it doesn’t really pass for more than a few seconds’ examination.

But there are others, like the one I saw yesterday:

This is more like it. It’s big, the size of a bumblebee queen, and it’s hairy, and its color pattern resembles those of a couple local species.

This is more like it. It’s big, the size of a bumblebee queen, and it’s hairy, and its color pattern resembles those of a couple local species.

This is a robber fly, a predator known to catch bees as well as other relatively large flying insect prey. There are a couple species in the East which are very similar to one another. Their larvae tunnel in rotten logs, preying even then on other larvae they encounter. After maturing, they perch in sun flecks on leaves or on more solid perches. The more common one in DuPage County appears to be Laphria thoracica.

Here’s another individual I photographed in July 2008 at Danada Forest Preserve.

Here’s another individual I photographed in July 2008 at Danada Forest Preserve.

Note the long black hairs on the top, front and sides of the head. If those were a dense solid yellow this would be a different species, Laphria grossa. I encountered those in south central Pennsylvania, and the impression was much the same. That beak probably could deliver a nasty bite if you grabbed this critter, but why would you want to? These take a longer, closer look to distinguish them from bumblebees. That beak is one giveaway. Another is the single pair of wings rather than two. Also, the perched fly frequently snaps its head to different angles, tracking possible prey. Bumblebees don’t do that. These robber flies are on my short list of niftiest local mimics.

Why the mimicry? One has to think it provides some protection from vertebrate predators. Also, these are among the largest of the robber flies, most of which are not mimics. That large size seems to slow them down, as they don’t fly nearly as fast as their smaller relatives. Perhaps the bumblebee coloration and speed leads prey to ignore them until it’s too late.

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