Friday, August 2, 2013

Aphids Making Gallons of Honeydew

 Ants have taken over a patch of milkweed at the nature center and they have brought their aphids with them.  The aphids cover the bottom side of every leaf, excreting their honeydew, and the ants protect them and get at least some of the honeydew.

It seems very pastoral in theory, but is the most chaotic and busy place around.
 While this picture seems to show the ant gently touching the aphids for a return of honeydew, it is only checking their safety in a very fast pass through the area.

With these aphids the ants don't seem to get the reward directly from the aphids at all.

But look at all the aphids under the 6 feet and legs of the ant.  And this is as big as they get, although there are many very little ones.

I measured the biggest aphids here at just under one millimeter.
 This little part of one leaf underside shows 106 aphids of different size.

The whole leaf had over 1,000, and there were 30 leaves on the plant, which means over 30,000 aphids on each plant.  I counted 22 plants in this group, so over 660,000 aphids in this colony.  Wow!
 Each aphid is withdrawing fluid from the plant, and excreting little drops of honeydew constantly.  Besides producing new babies and shedding their skin that is all they do.

Their drops of honeydew are tiny, but if they added up to just one water droplet in volumn in a week per aphid, that would be 660,000 drops of honeydew per week.  At 27 drops per teaspoon, that is over 7 gallons a week for this colony!

 Here you can see one little droplet just released by this litle gal.  I have turned the picture upside down so it is easier to see, so this droplet would actually be falling up to the leaf below it, onto the topside of the leaf.
 This picture is also turned over to see better, but the droplets are about to fall down, which is up in this picture.

With thousands of droplets falling onto the top surface of the leaf below you can imagine what a sweet, sticky, treasure trove the top of each leaf becomes.
 The ants spend most of their time eating the resulting droplets of honeydew on the top surface of the milkweed leaves.

Here you can see each tiny white spot is a droplet.  The ants get fat eating these, which they can take back to the nest to feed baby ants with.

The ants also have to spend a great amount of time chasing away other critters who are interested in this enormous food source.  They are not very successful.
I counted at least 5 ants on every leaf.  That means there are 150 ants per plant, and 3,300 on the combined 22 milkweed plants at any one time during the day.

But other insects come to feast as well.  There are at least 8 flies that I can count on each plant at any one time.  Lots of them flying all around.

Many are this red eyed species that is house fly size.  Its sponge/mop like mouth is picking up the honeydew, but while it eats even more honeydew rains down from the bottom of the leaf above, covering the fly with little specks of sweet dew.
Several other species of fly are also present, including this larger one.

The aphids are growing on the leaf up above and shedding their skins as they grow.  The shed skins fall as well.  One can be seen under the fly here. It is white.

After a few weeks of this there is mouldy honeydew, fly droppings, shed skins, and anything the wind blows onto the sticky surface.  It is a mess!
Wasps and bees are attracted to the sweets also.  They fly and walk rapidly from leaf to leaf to get the freshest honeydew. But the leaf top is now like a dirty parking lot.  Each white spot is a shed skin that has rained down from above, with much other debris as well.
This wasp has found a relatively clean spot to search.  Its antennae are constantly touching the surface looking for more.
In this picture a different wasp, a paper wasp, is eating the glistening honeydew along the edge of the leaf.

The entire top of the leaf is covered with this coating of sticky food.
Unlike the flies, this wasp is cleaning itself off after feeding for a while. Special combs on the front legs scrape off the other body parts.  It worked for several minutes doing this.

Aphids can be seen on the underside of the leaf to the left.  They are dropping more honeydew to the top of the leaf below.

With over half a million aphids and other food animals present, the predators show up.  Several Ladybugs were hunting and eating aphids while I was photographing yesterday.  The Ladybugs are too big for the ants, but there are so many aphids, they have little impact on their numbers.

This little milkweed patch is an extremely busy ecosystem.  Nothing can compare to it nearby for the  number of insects constantly entering and leaving, not to mention the over half million that live on it every day.


  1. Spectacular photographs! Thank you! Just learned of your website from the Mpls Audubon newsletter.

  2. Fantastic photos and descriptions. Amazing what all goes on just on one plant!