Tuesday, June 16, 2009

Edwards' Hairstreak Pupa

The term pupa refers to the third stage of complete metamorphosis that insects, such as the butterflies and moths, follow as they mature. Egg, larva, pupa, adult is the full sequence. Look for a brown lozenge shaped object in the center of the photo above. This is the pupa of the Edwards' Hairstreak butterfly, a rather rare and special resident of dry prairies and barrens.

I’ve mentioned the Mound Builder Ants, Formica integra, and their relationship with everything around them. In this instance, the ants have formed a mutually beneficial relationship with the Edwards' Hairstreak butterfly. During certain periods of their larval development, the Edwards' Hairstreak larvae produce a sweet secretion known as honeydew, which is highly sought after by the ants. To insure their supply of succulent sweets, the ants will care for the butterfly from the time it hatches from the egg to the time it emerges from the pupa as an adult.

The Edwards' Hairstreak larvae feed on the leaves of certain species of oaks. The ants escort the larvae into the tree and act as guardians as the larvae graze. Feeding takes place at night when the threat of being eaten by hungry birds is at its lowest. These leaves show evidence of predation by larvae.

When the larvae are old enough, the ants will harvest their honeydew. As dawn approaches, the ants herd the larvae to the base of the tree and secure them in a specially prepared chamber known as a bier. The larvae are fairly slow moving so a small tree with leaves close to the ground works best.

Sometimes the bier is a pile of soil and plant debris and other times it is simply a cavern excavated around the tree roots.

The larvae eventually pupate in the bier and the ants stand guard against any intruders until the adult butterflies emerge. The focus is a little bit off on some of these photos. It’s hard to take pictures down an ant hole.

The ants keep a constant check on the pupae.

Any threat to the bier will bring dozens of ants to the point of disturbance. I managed not to alarm the ants, except for the time my head pushed against one of the tree branches and a few ants charged out onto my scalp.

These butterflies will be emerging in the next week or two. I’ll show you the adults then.


  1. As an ant admirer, I love this post. The relationship of ants and blue butterflies is amazing and diverse. Thank you for sharing this.

  2. What a cool story! I'd not heard of ants tending to leps before...great pictures too!