In January/February we may be curious as to the size of the cluster and even if it is still alive. Lines of debris under the seams indicate live active bees and how large the cluster is. Looking more closely at the type of debris I recently saw on one of mine about 9 seams of debris with the two outer ones consisting of pale wax cappings which indicated honey stores being accessed on the outer frames. As they normally work from the inside out it means they only have about three frames of stores left, in this case on a shallow box probably a maximum of 9lbs left. This was in agreement with the light weight on hefting, and when I opened them briefly prior to adding a pot of fondant. The inner seams of debris were brown and crumbly, probably indicating brood rearing and cleaning up cells for that purpose.
The location of the debris indicates where the cluster is. If it is in the middle, assuming they started with sufficient stores they would have put it at both sides of the cluster and could still move to either side. Some of mine are at one side now, hard up against the wall of the hive. Does this mean they could potentially be isolated from stores on the other side if the weather turns cold? hefting in this case could be misleading. If you feel the need to add fondant, knowing which side they are on in advance could minimize disturbance if you have to move the crownboard round so the hole is above the cluster. If one of your colonies has no debris at all it either indicates your colony is dead, or that the mesh floor is so blocked with dead bees or debris that nothing is coming through. Investigate!
Sometimes one can see the circular discs which the pupae were sealed with, confirming that brood is hatching. I also spotted some wax scales, a bit unusual at this time of year as they prefer warmer weather to be wax building. However, it has been mild, and I even found some beige pollen loads dropped on the insert in the first few days of the new year when it was up to 12 degrees C.
If they have granulated stores, they sometimes suck the liquid and discard dry crystals, which show up on the insert. It seemed to be a good ivy year this last autumn so I would not be surprised to see crystals at some stage.
Pests and Disease. One of the main uses of the insert is to monitor for varroa. Ideally, the insert should be in for 7 days in winter as a single day drop can be misleading. I put the insert in December, prior to see if they need Oxalic acid vapourisation. After 24 hours on one colony there were no mites, great I thought! The second day there were 3, then 4, and 5 resulting in an average of 3 per day, so definitely worth treating. In the summer, with more activity, 5-7 days should give an idea of the average daily drop. I find icing sugar dusting is a much more accurate and quicker assessment of mite levels, for which of course the insert needs to be in place to catch the sugar and mites. Several treatments also require the insert to be in place, to keep the volatile treatments in the hive, such as Apiguard, and Oxalic Acid Vapourisation (OAV)and of course to assess the effectiveness of the treatments.
Have you ever examined the varroa more closely? After my OAV I found mites on their back twitching with white crystals of OA on their feet. You may see light brown juvenile varroa, or even varroa which have been chewed; indicating a level of hygienic behaviour in your bees. If this is the case you may also find bits of pupae in the insert indicating that either you have a bad attack of mites or that the bees are opening up mite infested pupae and removing them and the juvenile varroa. Other reasons for pupal pieces may be that the bees are starving and cannibalizing them, and sometimes they do this during Apiguard treatment, so depending upon the weather etc it may be worth investigating further.
Other things to look for on the insert include; small live wax moth larvae which sometimes fall through the mesh; wax moth droppings indicating how many and where they are so in warm weather you may be able to locate and kill them. In summer you may find bees and wasps on the insert, if this is a problem block the gap at the rear with some rolled up cloth or mesh. Ants are difficult to deter but making sure the insert is regularly cleaned and free of spilled syrup, honey, icing sugar etc will help keep bees, wasps and ants away. If you find mouse droppings or nuts or seed shells on the insert in winter, bees will not appreciate the disturbance and smell and mice will mess up any varroa counts you are trying to achieve so definitely exclude them by blocking the back.
Other signs of trouble to be looked for are chalk brood mummies and spots of brown dysentery, indicating something is not right (virus, Nosema apis, fermenting stores etc).
Other things. In summer you may see small, long legged mites running fast on the insert, these are harmless pollen mites, eating debris and nothing to worry about. Sometimes in winter if there is very cold windy weather, I try to reduce draughts for small colonies by putting the insert in while it lasts.
In the spring and summer with a bit of experience you can tell which flowers they are visiting from the colour of the pollen loads dropped through the mesh floor.
Last year in the hot weather, a couple of my colonies hung out the front and then moved under the mesh floor, also a clipped queen failing to leave with a swarm may move under the mesh, followed by the returning swarm. In both cases, after brushing them off into a box and returning them to the hive, putting the insert under the floor for a few days should solve the problem.