Leonard and I discovered several interesting ant mounds in a field to the east of our property on County Road 87 near Lookout CA (Modoc County). While watching the mound I discovered how aggressive those ants could be. It only took a few minutes, standing about two feet from the mound, before the ants were crawling over my pants and up my legs. Their bites were very annoying. I moved back and brushed off as many ants as possible before swooping in with a collecting jar (holding about a cup) to scoop up about 30 ants. Even in those few seconds my hands were covered with more ants. I whisked the ants off the jar and put it in my pocket.

Once back home I put the jar in the refrigerator for about a half hour. Chilling is a safe, easy and effective, if short-lived, method of anesthetization to enable the study of insects and to photograph them. The cold triggers insect chill coma – the threshold at which neurotransmitter activity comes to a halt. The results depend on the environment from which the insects were collected or reared and the insect’s species response to cold.

I believe the ants that made those mounds are members of the Formica genus – more specifically, I believe they are red mound ants (Formica integroides). Formica ants are large (4 – 8 mm long) with large heads and powerful jaws. Most are bicolored (red and black) but some are all black. They are aggressive and bite.

Red mound ant nests nests can be found under moderate cover or in open areas devoid of cover. The nests are built under and around a log, stump or rock or by direct excavation of bare soil. The nest may be covered or surrounded by some thatch.

The nest is initiated by a single inseminated queen. She digs tunnels and lays eggs. The workers that hatch are all females. These workers then continue to build the nest, gather food and tend to the queen who now devotes all her time to egg laying. In the summer reproductive winged drones (males) and winged queens are produced. The winged queens and drones fly and mate. The drones then die while the inseminated queens start new colonies.

When I took the ants out of the refrigerator, they were indeed not moving. Instead the ants were all dead and curled up. Even after a day of “recovery” there was no recovery. The ants were dead. Did I leave them in the cold too long? Was this a species that was particularly sensitive to cold? CJ Tanner in 2009 had studied cold anesthetization of F integroides without killing them.

A few days later I decided to try collecting more red mound ants to photograph. I remembered that the first time I never looked at the ants in the collecting jar after I put it in my pocket. I placed it in the refrigerator without checking the ants. There HAD to be enough air in the jar for so few ants. However, this time I determined that I would open the container a few times to be certain there was enough oxygen. As Leonard and I walked about the field searching for wildflowers, I kept “refreshing” the air in the sample jar every five minutes. At 20 minutes all the ants were again dead, having never come near a refrigerator. This time they had plenty of air and no chilling. What happened?

I have no idea why the ants all died within about 20 minutes. Ants in the Formica genus produce formic acid as an anti-predator mechanism. Once under stress did the ants produce formic acid in the closed container and kill each other. Or??

Any ideas to help solve this enigma?

Gallery | This entry was posted in Insects and tagged , , , . Bookmark the permalink.

2 Responses to Enigma

  1. usermattw says:

    What a mystery. I assume the jar was clean? Not even traces of detergent?

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