Monday, September 15, 2014

Ants and Scale Insects

If I’m just out looking around, I never fail to investigate anything that draws the attention of the Allegheny Mound Ants.  If the ants are involved, there is undoubtedly something of interest to be seen.

In this case, I was led to a colony of Scale Insects.  Scale insects spend most of their lives immobile on the branch of a tree and create a thick dome-like casing that hides their entire body.  They feed by drawing sap from the tree through a tube shaped mouth that is permanently imbedded into the tree’s bark.  These were feeding on Tuliptrees, Liriodendron tulipifera.  I’m going to go out on a limb here and call these the Tuliptree Scale, Toumeyella liriodendri.

The affected trees were all small and growing out in the open.  A large colony of sap draining insects could cause severe damage to a tree of this size.

Despite their protective covering, Scale Insects are plagued by many predators.  Fortunately for the Scales, the ants are on hand to ward off any potential threats.

Guard duty is not a free service.  It is a benefit resulting from the ant’s actions to protect a valuable source of food.  Like many sap consuming insects, some Scale Insects produce a sugary byproduct called Honeydew that is regularly secreted.  The ants are quick to imbibe this liquid as soon as it becomes available.  The ant on the right in the above photograph has an abdomen distended to a point of semi-transparency by honeydew.

Large Tuliptree Scales found during this time of year are all female.  They are just reaching the end of their year long life cycle and like this one, are soon to die and fall from the tree.  As the immobile females develop, they lose many of their extremities, but the three basic insect body parts are still recognizable.  In the above photo of the underside of a mature Scale Insect, the head is toward the top and the sections of the abdomen are still visible in the lower half of the body.

The female of this species holds the developing eggs inside her body until they hatch.  The newly hatched insects are then held inside the waxy shell until they have developed enough to strike out on their own.  The dark mass to the left is a mass of developing eggs.  Eggs hatch and young are released over a two to three week period.  When the last of the eggs has hatched, the female dies.

The young crawl from beneath the shell and spread out over the tree.  Once they find a suitable site, they will attach themselves to the bark and begin feeding.  The females will never move from that site.  Males will form a shell in which they will pupate next spring. Sometime in early summer, winged males will emerge and search out females with which to mate. 

Females typically grow a dome with a large oval-shaped base.  When conditions get crowded, irregular shapes are formed to fit available space.

The ants have gathered cedar needles and used them to form a temporary shelter at the base of the scale infested tree.  The ants will use this as a base as long as there is honeydew to be collected.

Construction of temporary nests is a common activity among Allegheny Mound Ants.  I’ve seen them make these shelters anything from baseball to basketball sized and use them for weeks or months before once again merging with the main colony.  I have yet to see any activity that gives clues to how the bounty collected by this satellite group is shared with the colony.  I may just have to camp out with the ants until I figure it all out.

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