Some April Insects

by Carl Strang

Insects began to appear during April’s warm spells. Inevitably I have been comparing my finds at St. James Farm Forest Preserve to my experience at Mayslake Forest Preserve, the site of my previous preserve monitoring. Some of the early insects at St. James Farm are shared with Mayslake.

The red admiral overwinters in the pupal stage.

The red admiral overwinters in the pupal stage.

Another early season butterfly is the spring azure.

Another early season butterfly is the spring azure.

Other species I never found at Mayslake.

The six-spotted tiger beetle prowls the trails at St. James Farm, as it does on many forest preserves. I was perennially surprised that I never found them at Mayslake.

The six-spotted tiger beetle prowls the trails at St. James Farm, as it does on many forest preserves. I was perennially surprised that I never found them at Mayslake.

One impressive insect I encountered at St. James Farm was entirely new to my experience. I first saw it flying, and I thought I was seeing a large bee fly or a fat bee. Then it landed.

It proved to be a beetle. The bumble bee flower beetle’s name reflects its impressive mimicry.

It proved to be a beetle. The bumble bee flower beetle’s name reflects its impressive mimicry.

This is a member of the scarab family, and it feeds from flowers, ripe fruits, and sap-exuding tree wounds.

Butterflies

by Carl Strang

Butterflies are the most conspicuous insects, and to the extent that they are representative, they are telling us that insects got through the winter in pretty good shape. Butterflies have been abundant and diverse this spring, both species that wintered here and ones that have migrated north. Earlier I mentioned red admirals in this context, and their congeners the American lady and painted lady butterflies have been showing up as likely migrants as well. A member of a species new to my experience appeared at Mayslake Forest Preserve last Thursday.

Obviously a fritillary, it seemed too big for a meadow fritillary and too small for other species of my acquaintance. Also, it lacked silvery spots beneath the hind wing.

My practice is to photograph doubtful cases when I can, and this time it paid off. The newcomer is a southern species known frequently to wander north, the variegated fritillary.

On Friday I saw 3 question mark and 2 mourning cloak butterflies.

One of the question marks, named for the pale silvery small markings on the underside of the hind wing.

That in itself is not all that unusual, as I have seen both species at Mayslake before. What seemed odd was, in this butterfly-rich spring, these were the first of both species I have encountered on the preserve. Both overwinter as adults, and back in March during the warm weather we experienced, I would expect to have seen them, especially with multiple sightings of both species happening now. What gives? Yet another little mystery to tuck away in memory.

Recent Insect News

by Carl Strang

Red admiral butterflies have attracted a lot of attention in recent weeks. We are seeing many more than usual this year. According to authorities, including Chicago’s Doug Taron in his blog, these are mostly migrants coming up from the south.

Red admirals have been appearing in clusters at Mayslake Forest Preserve. I am counting dozens on a typical lunchtime walk.

I wonder, though, how many are local survivors of the mild winter. It might be possible to find out, by doing chemical or isotope analyses of tissues. That method has been used, for instance, to determine where breeding birds spent the winter, but it would be an expensive study to undertake.

Another migrant which has begun to show up in greater than usual numbers is the American lady, a butterfly in the same genus as the red admiral.

Last week I saw a few syrphid flies which proved to be indistinguishable from one of the species that were abundant last fall.

According to references I accessed through the BugGuide website, both these and the autumn ones are Helophilus fasciatus.

I also photographed a small bee that is colored like a carpenter bee.

This may be the mining bee Anthophora abrupta. If so, the pale face makes it a male.

These have tunnel nests in clay banks. The most likely nearby location is the friary demolition site. When my back has healed to the point where I can be more mobile, I’ll see if I can find a colony there. That would confirm the identification.

Recent Butterflies

by Carl Strang

Earlier I mentioned that one winner in the winter survival sweepstakes appears to have been the spring azure. Another butterfly that apparently benefits from mild winters is the red admiral, and I have been seeing enough of these already at Mayslake Forest Preserve to regard them as another beneficiary in 2012.

Sometimes the red admiral can be seen at a flower or on territory, but often all you get is a flash of orange on an otherwise dark wing as the medium-sized butterfly flits past.

It’s too soon to tell with other butterflies. Last week I got the opportunity to photograph both genders of the wild indigo dusky wing, but they are the only two individuals I have seen to date.

The female of this species is somewhat brighter and lighter.

These skippers indeed often hang around Mayslake’s wild indigo plants, but their population reportedly has increased in recent decades as their larval diet has broadened to include other legumes.

The darker male wild indigo dusky wing is different enough that one easily could believe it belongs to a different species.

It seems I have been counting a few more black swallowtails than usual, as well, but again I need to see more before I will think they had greater than usual survivorship.

Literature Review: Butterfly Range and Diet

by Carl Strang

This week’s literature review note is about butterflies. Usually we just think of butterflies as delightful, beautiful bits of nature, but those qualities also attract the interest of scientists. The scientists in this case are J. Slove and N. Janz (2011. The Relationship between Diet Breadth and Geographic Range Size in the Butterfly Subfamily Nymphalinae – A Study of Global Scale. PLoS ONE 6(1): e16057. doi:10.1371/journal.pone.0016057). The butterflies they studied are 182 species in the widespread subfamily Nymphalinae. Our local members of this subfamily include such familiar butterflies as the mourning cloak, question mark and red admiral.

Mourning cloaks pass the winter in the adult form, hibernating in a sheltering refuge.

Slove and Janz were interested in seeing if there is a relationship between the diet breadth and the geographic range of these butterflies. They wanted to test a prediction that species which eat more kinds of plants have larger ranges. The diet of interest is not that of the adult butterfly, but rather of the caterpillar.

Mourning cloak caterpillars eat the leaves of trees in several families, so they would be regarded as having a wide diet breadth.

It turns out that the prediction holds. The point is that there are a lot of different kinds of plant-eating insects. Some have broad diets, others have narrow ones. How did this diversity come about? The possibility being considered is that some insects have large geographic ranges, in part because by eating a number of kinds of plants they can spread over the collective ranges of those plants. Over the course of time, circumstances such as climate change (interposing a glacier or desert, for instance), geological events (raising a mountain range or sea, for example) and chance isolations (a few representatives driven to a remote island by a storm, perhaps) divide a wide-ranging species into separate groups that no longer can interbreed. Each group may then specialize on the reduced menu of plants available to them, and over time can evolve into separate species. This is called the oscillation hypothesis, because over a long period of time it predicts an alternation between wide diets and narrow diets within a genetic line.

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