Collard Hill Egg Counts – 4th July

Hi everyone,

Today’s weather was really rather intimidating, with driving winds and the ever-present threat of rain.The forecast is not looking good, rain for the next week, which almost certainly means an official end to the Large Blue season.

Luckily the rain just about held off for the most part, allowing Dave Simcox, Sarah and I to perform our egg counts with relative ease. I forgot to get a photo of us, but if you imagine three people rooting around on their hands and knees looking for tiny eggs, you’ll have a pretty good idea of what our day involved.

The main news is positive. We will definitely have a population next year. We’re yet to calculate a full figure, and some more surveying is yet to be done, but we found eggs in every part of the site we checked today.

Egg surveying consists of using a semi-random method of throwing out 1m canes. The cane’s location then gives us a 1x1m grid in which to survey, in which we search for Thyme plants and Large Blue eggs. The site is split into 9 areas and each area is sampled between 15-30 times. Some samples contain no Thyme, so this method is also useful for giving a rough estimate of Thyme density across the site.

A full egg estimate can then be made by simply multiplying the average eggs found in an area by the size of that area.

The total egg estimate is likely to be lower than last years, but that by no means correlates directly with our population expectations (i.e. we’re not necessarily predicting that next year will have fewer adults than this year). One of the main reasons for this year’s poor population is the way in which last years summer drought really fried and dried out a lot of Thyme, hugely increasing the mortality of the Large Blue caterpillars dependent on it.
Ecosystems are generally full of checks and balances. This year’s poor number of LB caterpillars has likely meant the that the Myrmica Sabuleti ants will be doing well (which can be assessed by our ant surveys further down the line), meaning this years caterpillars will have plenty of food and a high chance of collection.
Density dependence effects also suggest that less dense egg laying means there will be higher survivability of caterpillar as competition between ‘caterpillar neighbors’ is greatly reduced.

So while we can’t account for the weather and climate of the coming year, the foundation isn’t looking too bad.

Thanks for reading!

Jono – The Large Blue Ranger

 

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