I live in Dąbrowa which means "oak forest", my garden is in Dębina which means "oak wood". In both places oaks are present, but nowhere near as proliferated as in Barycz Valley where I've spent my September vacation. There two out of three big trees are oaks (that's my personal, highly scientific "at a rough guess" estimation :o) ), many even reached status of nature monuments.
Since a lot of the area is nature reserve, even when the tree dies, its remains are left in place.
There are many large oaks, both dead and alive. The latter are favorite feeding and breeding grounds for great capricorn beetles. Barycz Valley is the center of population of those oak destroying pests in Poland. Moreover the beetles are stricly protected species, so even when the nature monuments fall prey to those vermin, they remain undisturbed by people. Actually, since the beetles prefer well lit places, trees that grow in separation from other trees (meaning they had enough place to grow big and effuse) are their likely primary targets.
Larvae start in the cracks of the bark, burrowing in it in the first year, but then dig deeper, not only into phloem (when that is damaged, it can prevent water and nutrients from reaching leaves, essentially killing the tree), but also even deeper, hard parts of the wood.
It takes three to five years to complete the growth, one larva can dig a meter long tunnel and there is never just one. The tunnels are also pretty wide, between thumb and two fingers, not counting the chambers larvae dig to turn into adult form, that can be even wider. That's the reason they attack big and old oaks - smaller tree would die before the larva can reach adult form.
Damage done by burrowing makes the oaks prone to further infections, f.e. by various fungi. Other insects can also use them as their homes. I've seen one tree where many holes were used by wasps, here is one with harvestman:
Larvae grow very big and fat, almost twice the size of an adult beetle, up to 10cm in length. The woodpeckers would love such meal, but because larvae dig so deep, they can only eat them when larvae are very young, still burrowing only in the bark.
Despite Barycz Valley being a place where there should be plenty of those beetles, I've spotted none and my brother found just one during entire week we've spent there. Here it is on hand to show its size:
It was sitting on a nature monument oak called Wawrzyn, growing in Wydymacz Nature Reserve.
The beetle on the photos is a female (males have much longer antennae and they also differ with their rear end) and it was not very mobile. Maybe because of the cold, or maybe it was the time when adults die already after mating and laying eggs, that would explain why we couldn't find any more of those beetles.
