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Thursday, September 20, 2012

Life, Death, Cooperation, & Coevolution... in a beetle

While out on a stroll yesterday afternoon, a group of parents and kids went across the fields of NBNC in search of Monarchs as part of our weekly Monarch Tagging Program.  A large insect flew across the trail.  For a moment, a dull-yellow glow made the creature appear as a bumblebee, but I quickly netted it and discovered it to be a very special beetle: the Sexton Beetle.

Burying Beetle (probably N. tomentosus) found at NBNC

Sexton Beetles (Nicrophorus sp.) are also known as burying beetles for a very important and unique ecological role they fill: burying dead things.  After finding a small carcass, the beetles begin to dig out a hole underneath it, allowing the body to sink into the hole and eventually be completely covered in soil.  The reason the burying beetle fulfills this ritual is to protect the carcass from other scavengers that could compete for the meat.  The beetle then strips the carcass of fur or feathers, lays eggs nearby, and nurtures its young as they feed on the rotting flesh, protecting them as they grow.  

Photo of mite by Tom Murray,
courtesy of bugguide
If this incredible life history wasn’t fascinating enough, the beetle we found was covered in mites.  While it would seem that mites could be harmful to the beetle, they actually have a symbiotic relationship.  These mites (Poecilochirus sp.) also feed on carcasses, but are unable to successfully travel from one carcass to another on their own.  Instead, they hitch a ride on the burying beetle!  In exchange for the transportation, the mites perform a cleaning service (a car wash, we could say) by removing any remaining meat on the beetle that could harbor bacteria.  (close-up picture of mite on the right)

Just in this one beetle that happened to fly across the trail, we can find death, birth, cooperation, and co-evolution.  Nature is always full of surprises and there is always more to learn, even from the tiniest of creatures.

Text and Burying Beetle photo by Larry Clarfeld

Thursday, September 6, 2012

"Giant" Backyard Discovery Returns!

one of the late-instar caterpillars

Before 2010, a Giant Swallowtail Butterfly had never been seen in Vermont.  Now, for the second consecutive autumn, this species has laid eggs in the Montpelier backyard of Abby Colihan.  A mild winter, sandwiched between two hot summers, has allowed the Giant Swallowtail to thrive in areas where it had been absent just a few years earlier.  

The range expansion of this species has limits, even in a warming climate.  The main host plants of caterpillars include those in the citrus family, and the only native host plant documented in Vermont so far has been Prickly Ash.  But Prickly Ash grows only in the Champlain Valley and southern parts of Vermont, so for Giant Swallowtail to lay eggs in Washington County, they need a little help.   Perhaps that is why the “gas plant” in Abby’s garden has been used two years in a row!

I counted a total of eight caterpillars on the small shrub; two were late-instar (older) caterpillars, and six were early-instar (young) caterpillars, which indicates that at least two female Giant Swallowtails laid their eggs there at different times.  At a glance, they look like bird droppings, but upon close inspection their intricate pattern is uniquely beautiful.  

Keep your eye out for adult Giant Swallowtails this month, as they may still be on the wing.  And one cold winter could halt their northward expansion.  Here is a photo of an adult that visited the North Branch Nature Center this past May:

Giant Swallowtail in the NBNC butterfly garden

 And here is a picture of one of the early-instar caterpillars, which was around 1/2 inch long:

An early-instar caterpillar

Photos and text by Larry Clarfeld