Cook vermicelli according to package directions. Drain and rinse with cold water. Drain again.
In a very large bowl, combine vermicelli, onion, green pepper, parsley, celery seed, oregano, and chives. Add Italian dressing. Toss to coat.
Add mayonnaise, shrimp, lemon juice, salt, and black pepper. Toss well to coat. Cover and chill in the refrigerator for at least 2 hours. If necessary, stir in a little milk until pasta mixture is creamy. Makes 6 side-dish servings.
You can prepare this salad up to 24 hours ahead; cover and chill in the refrigerator until serving time.
Carry this well-chilled salad to your picnic site in a cooler packed with ice.