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Thursday, October 3, 2013

Home sweet scat

In late August, Lewis and I encountered some coyote scat in the dunes with sandy tubes growing out of it.  Some of the tubes extended into the air (see below):


While on other pieces of scat, some of the tubes extended below ground (next picture, after tubes were exposed):


Neither of us recalled seeing tubes like this before and we were puzzled about what might be responsible for the tubes.  Was it a fungus?  Was it an insect?  We really didn't know what the possibilities were.
 
We decided to open a couple of the tubes to see if there were any clues inside.  First we discovered that the sandy tubes were bound by silk...and then Lewis found one of these (next picture)!


And after looking around a little more, we found a few dried, empty cases at the ends of several tubes.  The cases looked like this:


Well, we were pretty sure that the larvae Lewis found had made the tubes, but we didn't know what type of insect they were...and we didn't know if they were connected to the empty cases at the ends of the tubes.

We came back and did some research in books and online, but couldn't find any information about these mysterious insect larvae that built sand tubes in coyote scat.

So we decided the only way to possibly figure out what they were was to try to raise them.  We set up a small terrarium with sand and placed one scat with tubes in it and monitored it.  (Yes, most of our co-workers thought we were a little crazy!) 

The larvae were active and continued building their tubes.  Some approached the side of the terrarium where we could then see dense patches of silk.  Time went by, and at the end of September no adults had emerged.  We were starting to wonder if they ever would, and then on 1 October Lewis spotted an adult on the roof of the terrarium!

Here's what he saw:


They were moths!  This is Tinea occidentella.  It turns out that its caterpillars are known for feeding on coyote scat!

It's a very handsome moth.  Here are a few close-ups to highlight several features.  

One of my favorites was the white "pom-pom" on its head.  It's formally called a white head vestiture and is quite striking when photographed under a microscope!


Note the gold-flecked scales behind the head.


And the beautiful pewter-colored scales along the back:


We confirmed that the pupal cases we observed in the field belonged to this moth.  Here is one we found in the terrarium from which this moth likely emerged:


Notice that the adult moth left behind a few scales in the pupal case when it emerged.  The scales are triangular and look a bit like miniature gray gingko leaves.


I was wondering how the pupae got to the end of the tubes, and learned that in this family of moths the pupae are mobile!  They wriggle to the tips of the tubes just before they're ready to emerge as adults. 


Before this encounter, I had no idea there were moth caterpillars that fed on mammal scat.  But Powell and Opler (2009) provide an interesting description of larval foods in this family of moths: 

"Tineids do not feed on flowering plants, although one genus in the Palearctic mines in ferns; mostly they are generalist detritivores or fungivores, with a wide range of biologies from feeding on vegetable refuse, guano in bat caves, and detritus in spider webs to specialists on animal products such as scats, owl pellets, or feathers — some are capable of digesting wool, including several cosmopolitan species that feed on woolen clothes..."

And about Tinea occidentella specifically:

"The larvae live on natural keratinous materials such as feathers of bird carcasses and coyote scats." [They also found them infesting owl pellets.]


P.S.  Part way through this mystery we received assistance from several scientists at UC Davis' Bohart Museum of Entomology regarding the identity of the caterpillar for which we are extremely grateful!

1 comment:

Anonymous said...

most interesting - woke me up !!!