There is a specific health danger for ageing cats allowed outside: maggots. Skin disorders are more common in elderly cats. The skin is thinner and more easily damaged. From my personal experience – and the circumstances must vary – my then very elderly and sick tuxedo cat used to spend a lot of time in the backyard on cool grass. Looking back now I feel I made a mistake in not humanely euthanizing her earlier. She had chronic kidney disease which is not meant to be painful but I feel she was in pain.
Anyway, she’d spend hours on the grass snoozing. She became an ideal candidate for a flying looking for a host for her eggs. A cat’s fur that has become matted and soiled becomes a target for flies because of the possibility of organic matter being trapped in the fur upon which the hatched eggs can feed.
My cat’s fur was not matted or dirty. She was well cared for but she was very still for long periods. One day I noticed a group of white blobs in her black fur. I was disturbed. I quickly realised that they were eggs. They were very noticeable: the milky, white eggs against the black fur.

I dealt with the problem in a common-sense way: I combed through the area where the eggs had been deposited with a flea comb. This removed the eggs as you’d remove fleas.
There was no damage to the skin. It was a potential health hazard. The fly selects the fur of elderly cats as more suitable. And old cats are less likely to be able to keep their coat clean and free of fly eggs.
The preventative solution is to stop a geriatric cat from sitting on the grass outside for long periods. They can still venture out but there needs to be a regular check on those pesky fly eggs.
On a separate note, I’ve learnt that if a cat is very static and looks for a cool surface it is a sign that they are in pain. The cool surface chills the body which alleviates the pain. It seems that ill-heath in geriatric cats allowed outside is linked to fly eggs.

The worst kind of fly egg deposit onto a cat comes from the botfly, a parasitic animal. They may use an intermediate fly or e.g., mosquito to carry their eggs onto the host which can be a cat. The eggs are deposited on the skin from where they burrow into it to hatch. It is obscene but highly effective.
You might have seen the gruesome images and videos of veterinarians pulling a botfly larvae from the hole in the skin of a poor kitten. The larvae are large. One video shows a vet extricating a larvae from the nose of a young kitten. It must have been very unpleasant for the kitten and the vet!
