Calliandra, Blue Butterflies & Ants (part 3)

(click on photo to enlarge)

Most members of the family Lycaenidae exhibit a relationship with ants referred to as “myrmecophily” which means “ant-loving.” When the Ceraunus Blue/Marine Blue caterpillars reach the third instar they are apparently now large enough to form this association with ants. While at the North American Butterfly Association Spring Meeting in 2007, Harvard professor Naomi Pierce gave a riveting lecture on this relationship. I was determined to observe this phenomenon myself. Luckily several species of Lycaenidae were reproducing right outside our front door.

First I found a caterpillar and then waited for ants to find it. It didn’t take long to find this:

Ants tending a Ceraunus Blue caterpillar

The caterpillars measure about 5 mm at this stage so the ants are very tiny and are probably sugar ants since they were also observed visiting the flowers. The ants seem to be drawn to the rear end of the caterpillar so I did some research and found the following interesting information: these butterfly larvae all contain single-celled epidermal glands (pore cupola organs) which are thought to secrete substances which pacify ants. The word “pacify” seems to imply that the ants might otherwise consider the caterpillar a prey item. Second, the seventh abdominal segment of these caterpillars contains a “dorsal nectary organ” which secretes a nutritious substance for ants. There seems to be a mutual relationship here — the caterpillars provide nutrition for the ants, thus protecting themselves from becoming a meal for the ants. The ants, in turn, leave the caterpillars alone and also provide protection from other predators.

Ants partaking of a caterpillar’s sweet offering

The relationship gets even more interesting with the involvement of a third, sometimes visible structure called the “tentacle organ.” This organ is “eversible” extending out from the body when the caterpillar needs it and retained inside when it doesn’t. In the photo above you can just see the two whitish spots that resemble eyes near the end of the body. The ants are feeding just above them. In the photo below, you can see the tentacle organs expanded.

Tentacle Organs

The tentacle organs also secrete substances that attract ants but do so only when the caterpillar is alarmed. In my observations it seemed to be a distraction tactic. Whenever the ants went to the head area of the caterpillar, the tentacles were raised and the ants rushed down for their reward. This could be a way to keep the ants occupied and away from the “business” end of the caterpillar.

Ants occupied at the tentacle organs

Notice in the photo below one ant is at the head area while the other is going down to the extended tentacles.

If you’d like to read Dr. Pierce’s paper (The Ecology and Evolution of Ant Association in the Lycaenadie) on this relationship, here’s the link.