The third 節気 “sekki” division of the traditional Japanese calendar is:
‘awakening of insects’ (solar term)
The first “kō” microseason within this division is:
“sugomori mushito o hiraku”
Hibernating insects surface
That makes 蟄虫啓戸 the seventh microseason of the year!
It typically lasts 6~10 March.
This is #7 in a regular subseries of 365 Days of Japanese, where every five or six days I post about a Japanese microseason that has begun around the same date as the entry. I am taking all information from the list of 72 in this article. There is also a 36 microseason list here, which may be more authentic (rather than being based primarily on Chinese sources).
Image credit: D. Gordon E. Robinson, from the article here.