roaming the wilds of south west Surrey
In summer 2015, we built a wildlife stack out of pallets, with a double hedgehog house at the bottom and lots of spaces for various insects. I have spent many happy hours since then watching the many insects that it attracts, from mason and leafcutter bees to the tiny, jewel-like wasps which parasitise their nests. This spring, though, I’ve noticed a number of new visitors, and I’m a little trepidatious, to be honest. There have been a number of large wasps, which I’m pretty sure are queens of our common wasp, Vespula vulgaris, going into the largest diameter bamboo canes. They stay in there for ages (upwards of twenty minutes, sometimes), eventually emerging to fly off. What on earth are they doing in there? The only thing I can think of is that they’re stripping the plant material from the inside of the bamboo cane, to use for building their nests. I hope the nests aren’t too nearby, I must admit. I am very slowly overcoming my lifelong phobia of wasps, and can now share the garden with them quite happily as long as they don’t land on me. There are LOADS around this year so far; during the warm spell a few weeks ago, the garden was full of them, and as long as they’re just going about their business, I don’t mind them at all. A nest in the garden/house would be a step too far for me, though, I think, so I really hope that’s not what’s happening. 😦
Anyway, here is a video of the queen doing her thang. And a picture of the wildlife stack and a couple of the less scary visitors to it. 🙂
I like to think I’m fairly observant when I’m out and about in nature. So how on earth had I never noticed an Oak Apple until a few days ago, when now they are everywhere I look?? I’ve noticed Marble galls before, and read about galls, but these are so large and colourful, I just can’t believe I’ve missed them. I think this must be an especially prolific year for Oak Apples, because today when I walked at Frensham (with the intention of looking for galls to photograph), the trees are covered in them! This particular tree looked like an apple tree at harvest time.
A bit more about galls today. Galls are growths on plants caused by parasites; wasps or flies, often, but also fungi and even bacteria. The galls are actually formed by the plant itself, influenced to do so by chemicals released by the parasite. The mighty oak tree supports over 280 species of insects, including 79 gall-forming species. Some of these are so tiny that you wouldn’t notice them unless you knew what to look for, and others are noticeable by their weird forms and colours. The thing that fascinates me about galls is that a huge tree, with a lifespan of centuries, can be controlled and manipulated by a microscopic larva with a lifespan of a few months. As an example, the wasp that causes the Marble galls I showed yesterday lays her egg in the bud of a Sessile or Pendunculate oak (our two native species). When the egg hatches, the larva releases chemical messengers which instruct the tree to form a structure around the larva, providing it with food and protection. This structure is nothing like what the tree would naturally produce; the larvae rewrite the tree’s blueprint for its own tissues, co-opting the tree’s resources to provide the perfect nursery. The gall shape depends on the species of parasitic insect, but is always the same for that species, varying from tiny, doughnut-shaped Silk Buttons, or the spaceship-shaped Spangle galls, right up to the gall in today’s picture, the multi-celled Oak Apple.
The other interesting thing is that oak gall wasps have alternate generations, one sexual (ie male and female mate, then the female lays eggs) and one asexual, or agamic, in which all the insects are female, and don’t require a male to fertilise their eggs. These generations look completely different to each other, and have different behaviours and sometimes host plants. In the case of the Marble gall wasp, the male and female wasps emerge from small galls on the non-native Turkey oak, and set off to find a native oak tree. There they mate, and the female injects her eggs into the buds. The larvae grow inside their gall nursery, eventually drilling their way out (leaving the tiny holes you can see in vacated galls) and emerging as the asexual female generation. She flies off in search of a Turkey oak, lays her eggs there, and the cycle begins again. For the Oak Apple gall wasp, the sexual generation of Biorhiza pallida emerge from the gall, and the mated female lays her eggs in the roots of the oak. These form little marble-like galls, from which emerge an asexual generation of females, which lay their eggs on the twigs, and it starts again.
There’s another chapter to this strange tale… the many species of insect which parasitise these parasites! There are inquilines, who are basically squatters; moving in without persmission and often hogging the resources of the gall larvae. Then there are the parasitoids, who are the really scary ones; their eggs are laid directly into the larvae, and they eat their host from the inside out. But maybe I’ll save that for another day, and leave you with a picture. 😉