Blowflies (Calliphoridae) and vacuum-packed ham In a few cases blowfly maggots have been reported from vacuum-packed ham. The possibility of egg-hatching and larval development in the product was analysed. In experiments no hatching of blowfly eggs on vacuum-packed, boiled, sliced ham occurred. However, the eggs are not killed immediately; 1–4 days after the packing, they are still viable and when the wrapping is broken, hatching may occur. After a stay of 7–10 days on vacuum-packed ham, the viability of the eggs seems lost. In the actual case the risk of oviposition by blowflies on ham in the cannery and succeeding larval development in the product is considered to be very low.