31 August 2024

After yesterday evening’s rainbow a “triangle fly” landed on our dining room window and spun its body slowly like a top. Google Lens identified it as genus Rhagoletis, a member of the fruit fly family Tephritidae.

There are about 25 species of Rhagoletis native to North America, each with its own host fruit. Those who eat the fruits we grow commercially, such as cherries and walnuts, are considered agricultural pests.

Since my photo shows the bug’s underside, Google Lens picked up on the yellow body and identified it as the walnut husk fly, Rhagoletis completa, though it may have been a different species such as the closely related Rhagoletis suavis. There are black walnuts in Pittsburgh’s parks so these species are possibilities.

Here’s a topside view of Rhagoletis completa.

Adult female Rhagoletis inject their eggs into the host fruit so that the larvae have something to eat when they hatch. If you open an infested fruit it looks like it has maggots. Here’s a walnut husk (yes, it’s a fruit) with R. completa larvae in it.

Perhaps that’s why we occasionally see rotting black walnut husks on the ground.

Rhagoletis are preyed upon by jumping spiders!

Some species mimic jumping spiders. The wing-waving apparently deters the approach of jumping spiders, important predators of the flies. Other species have brightly-patterned bodies, and may mimic wasps.(3)

“Spider predation has been intense enough to mold the evolution of prey characteristics: predation by salticids (jumping spiders) has shaped the morphology and behavior of some tephritid flies. Their wing markings resemble the pattern of the legs of jumping spiders; the flies also wave their wings in a fashion that appears to mimic the agonistic behavior of salticids – making them ‘proverbial sheep in wolf’s clothing’.”(8)

— bugguide.net: Rhagoletis account

Could this native North American jumping spider be a predator of our Rhagoletis flies? Do you see a resemblance between its angled legs and the pattern on the fly’s wings?

The triangle fly has opened a whole new area of inquiry.

22 August 2024

Right now fall field crickets (Gryllus pennsylvanicus) are in the midst of their breeding season. Like songbirds the males sing to attract a mate.

It’s relatively hard to find a singing cricket because the male is on the ground, probably hidden by vegetation, and facing the entrance to his burrow. He rubs his modified leathery front wings, called tegmina, to make his chirping sound.

The burrow entrance provides an echo chamber that amplifies his sound and, if his chirping attracts a predator, he can quickly zoom underground for safety.

Older male crickets are better at chirping than younger males so they attract more females. She approaches …

… and they mate.

She will use her ovipositor to inject 50 eggs into the soil.

And then they’ll go off to eat the seeds of their favorite foods, many of which are invasive weeds including: Smooth crabgrass (Digitaria ischaemum), lamb’s quarters (Chenopodium album), English plantain (Plantago lanceolata), switchgrass (Panicum virgatum), common ragweed (Ambrosia artemisiifolia) and chicory (Cichorium intybus). [list from Wikipedia]

Did you know that the cricket’s chirp can tell you the temperature? Count the number of chirps of a lone cricket for 15 seconds, then add 37. That should tell you the temperature in Fahrenheit … probably. If it doesn’t, I like to imagine that the burrow entrance is colder or hotter than the ambient air.

Read more about the cricket’s chirp here at the Songs of Insects.

p.s. Did you ever have a cricket in your house? In my experience they are really hard to find unless they’re in the corner of a gleaming white bathroom and you’ve moved everything out of the way to find the cricket in the corner.