Our grassland around Phase 1 is full of botanical variety and is awash with colour in the summer. It is also a haven for countless species of invertebrates using each plant species for various purposes as part of their lifecycles. An interesting find from last week by our Warden, Paul Bennett was this gall on a hawkweed species, or Hieracium sp. to be scientific. The hawkweeds are an incredibly complex genus, with thousands of named species, many with only very slight differences between them.
The gall (a chemical response from a plant stimulated by the presence of a causal organism) is caused by a wasp of the Family Cynipidae and for anyone who follows this blog regularly and has seen the oak galls from a few weeks ago, this wasp is in the same family as the causal organisms of the oak marble, oak spangle and oak apple galls. The wasp is known as Auracidea heiracii and in the imago (adult) form is tiny, at only 2-3mm long. It is however, the larva that makes the hawkweed it's home and forms the gall. After hatching from it's egg, it feeds inside the hawkweed stem, before pupating.
Most Cynipid wasps have two generations per year, a sexual generation containing both male and female insects, which must mate in order to reproduce and a parthenogenetic generation, which contains only females which do not need to mate to reporduce.
Here is the Auracidea hieracii gall on the stem of a hawkweed plant from the Phase 1 grassland. They seem to be fairly common, with several being found over the last week.