As anybody who follows my twitter feed will know, wildflowers are a constant source of inspiration and fascination for me. Here are a few of my favourite finds from 2018
This is a quick roundup of some of my favourite insect encounters of 2018 – there are some beautiful and highly varied species in the UK which reward the close observer!
Along with the holly and the ivy, mistletoe is one of those species which is intimately associated with the festive season. You might almost say it is a hemi-parasite on the cultural Christmas tree…
A small group of us undertook some voluntary tree climb surveys in Clumber Park before Christmas 2018 to look for roosting bats. One of the trees which I climbed was an old lime set amongst younger trees and this had some beautiful examples of mistletoe right in the top of the crown. It seemed a good opportunity to share some photos and ecological insights into this fascinating plant.
Mistletoe is a obligate hemi-parasite – it is only found growing attached to trees. This is because it is partially reliant on the tree for sustenance – it taps into the xylem system of the tree to source water and soil minerals. It does however phytosynthesise itself which makes it only a half or partial (hemi) rather than full parasite.
Mistletoe does not have roots, rather it grows on the surface of the branch and encourages the tree to grow around it. This gives the illusion of it penetrating the bark to reach into the branch and take its sustenance, but the truth is much less aggressive.
The main ‘mistletoe’ heartland in the UK is the south-west midlands – this is particularly around Herefordshire, Somerset, Monmouthshire and Gloucestershire and up as far as Warwickshire. It is however found sporadically in many other locations around the country – close to Grantham, the village of Bottesford seems to be unusually well covered. The origins of these more isolated pockets of mistletoe is often unclear, but many old parklands and country estates tried to establish colonies in the past and it may be that these give rise to local populations away from their stronghold. Given the history of Clumber, this might be a good explanation for the colony I found!
Mistletoe expresses a significant preference for some tree species over others – cultivated apple is the most well-recorded host with lime (like the Clumber tree) coming in second. Other species include hawthorn, poplar, maple, and willow. They have however been recorded on hundreds of tree hosts and some have particular cultural significance – mistletoe growing on oak was the centrepiece of a Celtic religious ceremony.
Most fruit and berry-bearing species in the UK owe a debt to wild birds who disperse the seeds, but mistletoe has a particular reliance upon them. Some species, such as the aptly named mistle thrush, will eat the seeds and excrete them again – often whilst perched on a branch. Not only does this deliver the berries right to the branches but it comes with its own ‘glue’ in the form of the droppings, to help hold the seed in place whilst they develop. Other species such as blackcap wipe the seeds from their beak directly onto the tree – a cleaning action which is coincidentally very likely to deliver the seed to an ideal spot for germination.
This means of spreading seed is the reason for the common name of mistletoe – ‘mistle’ derives from the Anglo-Saxon word for dung and ‘tan’ derives from the word for twigs. The latin is Viscum album – the album meaning ‘white’ and relating to the colour of the berries.
Small patches of mistletoe often go un-noticed or overlooked – either because it is concealed by the dense leaf cover of its host tree, or because people are simply not looking up and around to spot it. Winter is an ideal time to spot this fascinating species – keep your eyes skywards and look out for the characteristic globes of vegetation suspended bauble-like in the branches!
If you want to find out more about mistletoe – its ecology, natural history, cultural significance, distribution and commercial importance – I would highly recommend reading Jonathan Briggs’ Mistletoe Diary blog!
Thermal imaging technology works by recording the infra-red energy emitted from surfaces – this doesn’t rely on a light source like typical infra-red photography, but instead measures the radiation given off by both living an inanimate objects. The camera can measure the temperature of these items and display a ‘thermal’ image which shows the gradation and variation between different objects within the field of view. In simple terms – it can show a hot object as white/red whilst cooler objects would be shown as green or blue.
In mid-summer, social bees produce a high density of very busy insects in the nest, so it was no surprise that they stand out a mile on a thermal camera! It was also exciting to be able to understand what individual bees had been doing – for example their temperature signature differentiated those who had recently returned to the nest from those who were standing guard and checking in new arrivals.
Wild Honey Bee Nest
We often encounter honey bees when out looking for tree roosting bats in woodland and this was a prime example! Whilst honey bees are often kept in hives, they can establish wild colonies in features such as this.
I took the following images around sunset so the tree itself was cooling but you can immediately see just how hot the inside of this tree cavity is compared with the surrounding wood. The temperature reading inside the nest was 33 degrees Celsius, whilst the surrounding tree barn dropped to around 25 degrees.
Even at sunset, honey bee workers were still returning to the nest and you can see the white-hot glow of these warmer bees compared with the much cooler bees at the entrance. What is also interesting is the pattern of heat in these recently-flown bees – the flight muscles are in the thorax where the wings are attached and this part is much hotter than the abdomen as you can see more clearly in the video below.
The thermal image gave a nice opportunity to watch guard behaviour in action – some honey bees will take the roll of guarding the nest entrance, positioning themselves on the edge and checking returning bees to ensure that they are welcome. The thermal footage clearly differentiates those bees who have recently flown from those which have not, and you can see the much cooler guard bees intercepting the warmer returning workers as they pass by.
If you’re interested in guard behaviour, you might also like this post from a couple of years ago regarding this behaviour in hornets!
These images and videos come from a bumblebee nest which was situated underneath a loose cobble in the courtyard of our office.
I think the bumblebees are either white-tailed (Bombus lucorum) or buff-tailed (Bombus terrestris) bumblebees – this photo shows one of the worker bees returning with well laden pollen baskets.
The thing that I found most surprising on the thermal footage to see just how hot this cobble got compared with those around it, even though the nest is buried beneath! I assume this is due to the heat rising with the warm air from the next and heating the stone as it passed by.
As with the honey bees, you can see how much warmer the active bumblebees are compared with their environment. Bumblebees have a good degree of control over their temperature. The hairs on their body provide some insulation and they can use their flight muscles – uncoupled temporarily from their wings – to warm themselves up before taking off. This uses the same technique as they use for buzz-pollination of some flowers. This video gives an idea of just how much heat these muscles can generate, allowing some bumblebees to remain active through the winter, flying at temperatures of just 10 degrees Celcius. You can read more about bumblebee thermoregulation here!