Sunday, May 06, 2007

Yesterday I saw an ant pick up an aphid and fly away with it

Okay, maybe this isn't earth-shaking news, but when I think of E. O. Wilson I still think of The Ants before his other books, and I've never seen this happen before. Wandering on a trail in San Mateo County, I came across a goldenrod-ish plant with brown aphids clustered everywhere. On the very top was a single, winged ant grasping a green aphid in its mouth. After a minute or two, the ant flew away with the aphid.

Ants eat other insects but are also known to tend aphids and collect a type of "honeydew" from them. Worker ants are wingless, but dispersing, reproductive males and females can fly. The only thing that males care about is finding females, so the ant I saw was a dispersing queen. Also, aphids can reproduce asexually, and like Tribbles, the females are born pregnant.


1. The new queen has already mated and was taking an aphid to found another aphid-tending colony. She'll settle down at a host plant with no aphids, which therefore has no existing ant colony that would quickly terminate her command.

2. The ant queen has already mated and is acting somewhat like her relative the wasp - she's carrying a one-time food source for herself as she founds a new colony somewhere.

While I think #1 is cooler, I suspect #2 is more likely. I think I would have heard of ants transporting aphids before. While only one of the hypotheses is correct for the ant I saw, both could be true as a general matter. But more ants species are likely to hunt insects than herd them, so my guess is the aphid is now lunch.

IMPORTANT UPDATE TO THIS IMPORTANT ISSUE: I talked to a butterfly biologist about this. He said he had no knowledge about it, but "when it comes to insects, anything is possible."

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