Cluster of tiny spiders.

Cluster of tiny spiders.

Observation - Cluster of tiny spiders. - UK and Ireland. Description: Found hundreds of tiny yellow spiders with dark coloured marking at the rear end, clustered tightly together in a ball on our outdoor windowsill. If I gently blow on them, they disperse in different directions all over the web; some descending down the sa

Found hundreds of tiny yellow spiders with dark coloured marking at the rear end, clustered tightly together in a ball on our outdoor windowsill. If I gently blow on them, they disperse in different directions all over the web; some descending down the same strand etc. After a while they all cluster back together again.

I've been theorising that they must be newly hatched, and maybe cluster to together to help retain heat, and possibly as a survival mechanism to make themselves look bigger than they are to potential predators (similarly to a murmeration of starlings).

Any ideas what they are, and if any of my theories are valid?