In Baldur's Gate, Taerom Fuiruim in Beregost will buy it for 500 as long as they don't make the agreement that he will make one set of ankheg plate mail and only during a ten-day period, as the shells start to rot after ten days. Ten days later, the plate is ready and, after that, it is no longer possible to sell any shells. (This is not true in BG:EE, where you can still sell ankheg shells or have him make another set of ankheg armor after the first.)
Note (Baldur's Gate): Taerom Fuiruim buys all of the ankheg shells in your party inventory (including party members). To get the most bang for your buck, if you have more than one shell, is to send your party leader to Taerom Fuiruim and send the other party members with shells to a barrel (recommend the barrel just west of the Jovial Juggler) and store the extra shells in the barrel. When you only have one shell in the party inventory, have leader speak to Taerom, make the 500 deal. Switch to a party member by the barrel, get one shell, switch back to leader and rinse repeat until you've sold all of your shells. Update for BG:EE V1.3 This note no longer applies; Taerom Fuiruim will buy a single shell per conversation (instead of cleaning out your entire party's inventory with a single sale).
Tip: when traveling back to Beregost to sell the shells, go one area south of Beregost, then travel immediately north so you appear at the south entrance by the Jovial Juggler. It's a short walk to the barrel & Taerom Fuiruim.
|“||The Ankheg is a burrowing insect-like creature between 10 and 20 feet tall, found mainly in forests or agricultural land. They are covered in shells made out of a substance called chitin which is extremely tough and very light. The size, the weight and strength of the shells make them highly sought after in many situations, including the creation of armor.||”|