I have seen these on my hands recently and I am wondering what they are. Urban Setting. South Central Pennsylvania.
This appears to be a bird mite (or possibly rat mite) in the genus Ornithonyssus of the parasitic family Macronyssidae.
Credit: user Aewills on bugguide.com
The mites are distinguished from most other common, structural species by the very long legs and very long mouthparts. These long, pointed chelicerae and palps stick well out in front of the head region. The 8 legs are very long and well separated, allowing for good mobility by these mites. The body is oval, with the thorax and abdomen combined to a single segment without separation. The color is light grayish in unfed mites to reddish orange in mites recently having had a blood meal. The fowl mites often seem to have a patchy, mottled appearance of dark areas.
Distinguishing between species is difficult.
As for knowing the specific species, citybugs.tamu.edu suggests:
Distinguishing between different species of Ornithonyssus mites to determine whether birds or rodents are the likely source is difficult and requires special expertise.
- chelicerae shape
- dorsal plate breadth and degree of dorsal coverage
- spiracle present between legs
- genitoventral plate width
- sternal plate shape and presence of setae
(see the linked post for pictures and more detail).
Regarding their affects on humans:
From Penn State Extension:
Bird mites have piercing mouthparts that enable them to take blood meals from their bird hosts. Although the mites will inadvertently bite people, they cannot reproduce without their bird hosts...
As the mites search for an alternative host, they will crawl onto the skin and conduct an exploratory bite to test the appropriateness of the host. The mite will move on, possibly trying the host again, but will not feed. These bites are felt as a “prick” and a resultant rash and itching, sometimes intense, will occur. Some individuals are apparently capable of sensing the crawling of the mites on the skin. The irritation produced by the bite is enhanced by the injection of the mite’s saliva that can cause a localized histamine response.
Remove birds (and especially nests) from on or near the building. Check for any holes in your building that could be large enough to allow birds inside. Again, these mites need birds to reproduce, so if you eliminate the birds eventually these will disappear. See PSU Extension and Central Extirminating Co. for more suggestions.