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The Gall of Those Ants!

Updated: Apr 29, 2022

In 2010 a variety of oaks and some shag bark hickory trees were planted in an old corn field located on the corner F and FA. This is up Bliss Road past Grandad Bluff on the way to Upper Hixon. The trees, however, never grew well mostly because of heavy deer browse. In 2016 the trees began to be protected with six foot high cages and since then they have thrived. Many have grown out of the cages beyond the reach of deer and have had the cages removed and tubes or small cages added to prevent damage to the trunks by deer rub. The goal is to have a closed canopy forest. Here is an interpretive sign that was recently put up at the site:

Oaks are extremely valuable trees in a forest ecosystem. A recent book by Douglas Tallamy, The Nature of Oaks, pays homage to the wonders of this magnificent tree. In fact, Tallamy calls oaks a keystone species, meaning that without this tree many other parts of the ecosystem would collapse. Oaks provide food for over 500 caterpillar species, far more than other trees. These caterpillars, in turn, provide much of the calories and nutrition for hungry birds that migrate through and breed in our area. And a lot of caterpillars are needed- it is estimated that it takes 6000-9000 caterpillars to raise a brood of 5 young chickadees! Here's a bird nest (possibly a chipping sparrow) on Skemp 2 this year:

Acorns produced by oaks also feed a wide variety of animals. Those produced by bur oaks (Quercus macrocarpa), also known as mossycup oaks, are the largest acorns of any North American oak and are favored by many animals as food because of their size and sweet taste. Bur oaks can live up to 400 years. Here are some bur oak acorns already being produced by the young trees just getting started on Skemp 2:

The acorns are food for wildlife only if weevils don't get to them first. About 30% of acorns are eaten by weevils. Have you ever noticed that some acorns feel lighter than others and that on close inspection have a small hole? These have been invaded by weevils. They grow by eating the rich pulp of the acorn then burrow out leaving the shell behind. Sometimes it's not obvious that an acorn has been affected by a weevil and some use the float test to check. Healthy, unaffected acorns will sink in water while those that have had a weevil in them will float. Interestingly, the empty shell is sometimes used by tiny ants from the genus Temnothorax as a home.

Some might have also noticed small warty growths on oak leaves and bumps on the stems. These are called galls and are caused by cynipid gall wasps. Most of the time they do no harm to the oak tree. There are over 800 species of cynipid gall wasps in North America and most of them favor oaks. They are small but pack a punch when they lay an egg in or on an oak leaf or branch and then release a slurry of hormones and chemicals to induce the trees into making the gall which serves as a secure home for the developing larvae while also providing it with food. Here are galls on oak leaves on Skemp 2:

But, despite these cozy homes, cynipid gall wasps themselves often fall prey to other insects called gall wasp parasitoids many of which, like their prey, are tiny wasps themselves. To provide further protection some galls come with a dense fuzzy fur like this hedgehog gall found on Skemp 2:

Others induce the oak gall to secrete a sweet sugary substance which is attractive to ants which then, as Tallamy describes, act as "bodyguards" for the larvae by fending off any would be predators. Here's a picture from Skemp 2 of galls with ants:

Unfortunately, oaks are not reproducing well and are slowly being replaced in the forest by other less valuable trees. It is estimated that oaks made up 55% of the forest in pre settlement times compared to 25% today. And of the 91 species of oak found in North America, 28 are on the verge of extinction. We hope the oaks on Skemp 2 continue to thrive well into the future.

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