Ooh, insects and parasites are my favorite. Such a shame there isn't more. Perhaps I'll draw some sometime >:)

You might want to check out these pixiv tags:

寄生虫 [parasite]
寄生 [parasitism]
蟲姦 [intercourse with insect]
苗床 [seedbed] - characters being used for "birthing" insects, parasites, etc
サナダムシ [tapeworm]