One night in September of 2004, I was watching my favorite Odontomachus clarus nest When I noticed an Odontomachus worker carrying a Brown Lacewing back to the nest.
The ant would proceed a few inches, then stop. She’d release the Lacewing and walk around it. She’d sometimes seem confused, as if she needed to re-find the Lacewing. When she did relocate the Lacewing, the ant would strike at the Lacewing with her trap-jaws, almost as if she were capturing it for the first time.
It was interesting to see the Odontomachus with the Lacewing, and to wonder how the ant caught the Lacewing initially. I would have thought the Lacewing would just fly away when the ant approached. But perhaps one of the advantages Odontomachus’ fast jaw-strike is that the jaws would enable the ant to catch insects that would otherwise be too quick. Like a fly-swatter works better than your bare hands when you chase houseflies.
So, while most ants that rely upon grappling to catch prey might be too slow to catch a flying insect, the Odontomachus jaws would be able to strike the flying insect before it could move to take off. I’m not sure if that’s what happened with this Lacewing, but it makes a nice story.
I was also puzzled by the repeated attacks – the batterings, almost – that the Odontomachus performed on the Lacewing. These occurred after the ant had captured the Lacewing, and while the Lacewing was not visibly struggling.
I read in Thomas Eisner’s book Secret Weapons that at least some Green Lacewings secrete a chemical, skatole, from thoracic glands when they are disturbed. Skatole is one of the primary chemicals that give feces their…um…distinctive odor. It’s not a long stretch to assume that the related Brown Lacewing would also secrete defensive chemicals.
In addition to skatole, Blum etal (1973) and Zhu etal (2000) have also found Tridecene in the defensive secretions of Green Lacewings. Tridecene is one of the compounds that various stinkbugs and beetles use in their defensive secretions. Both papers indicate that they found the defensive secretion from Lacewings to be a deterrent to ants.
So…here’s what I’m going to speculate about the Lacewing and the Odontomachus after the initial capture.
I wonder if the Lacewing was emitting defensive chemicals from its thoracic glands, and the Odontomachus was reacting to the compounds. Odontomachus dropped the Lacewing due to the secretions, then had to re-locate/reacquire the Lacewing. The Odontomachus may then have hit the Lacewing numerous times with her jaws either in an effort to make the Lacewing stop secreting the chemicals, or as part of a stereotyped recapture-behavior.
I wonder further if the length of the mandibles in Odontomachus makes it easier for them to prey upon insects that have defensive secretions. The mandibles might act as ‘salad tongs’ to hold the prey at a distance.
In a sense, the jaws of trap-jawed ants are ranged weapons, enabling the ants to attack insects that are further away than ants with more conventionally shaped jaws can.
Sources:
Blum, Murray S., J.Bruce Wallace, Henry M.Fales, (1973). Skatole and tridecene: Identification and possible role in a chrysopid secretion. Insect Biochemistry. Volume 3, Issue 12, December 1973, Pages 353-357.
Thomas Eisner, Maria Eisner, Melody Siegler (2007). Secret Weapons: Defenses of Insects, Spiders, Scorpions, and Other Many-Legged Creatures Paperback – Illustrated. Belknap Press: An Imprint of Harvard University Press. ISBN-10 : 0674024036. ISBN-13 : 978-0674024038
JUNWEI ZHU, RIKARD C UNELIUS, KYE-CHUNG PARK, SAMUEL A. OCHIENG, JOHN J. OBRYCK and THOMAS C BAKER. (2000). IDENTIFICATION OF (2)-4-TRIDECENE FROM DEFENSIVE SECRETION OF GREEN LACEWING, Chrysoperla curneu. Journal of Chemical Ecology, Vol 26, No 10, 2000.
